mirror of
https://github.com/golang/go
synced 2024-11-24 10:40:10 -07:00
big: ~8x faster number scanning
- better number scanning algorithm - fixed a couple of bugs related to base interpretation - added scan benchmark - added more test cases and made tests more precise - introduced Int.scan method matching nat.scan - refactored Int.Scan; now uses int.scan - refactored Int.SetString; now uses int.scan There is more potential, this was a fairly simple change. gotest -test.bench="ScanPi" before/after (best of 3 runs): big.BenchmarkScanPi 1000 2024900 ns/op big.BenchmarkScanPi 10000 257540 ns/op R=chickencha CC=golang-dev, rsc https://golang.org/cl/4527089
This commit is contained in:
Robert Griesemer
parent
16dbf2182c
commit
ce2701b2b0
@ -8,6 +8,7 @@ package big
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import (
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"fmt"
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"io"
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"os"
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"rand"
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"strings"
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@ -375,11 +376,48 @@ func (x *Int) Format(s fmt.State, ch int) {
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}
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// Scan is a support routine for fmt.Scanner. It accepts the formats
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// 'b' (binary), 'o' (octal), 'd' (decimal), 'x' (lowercase hexadecimal),
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// and 'X' (uppercase hexadecimal).
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func (x *Int) Scan(s fmt.ScanState, ch int) os.Error {
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var base int
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// scan sets z to the integer value corresponding to the longest possible prefix
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// read from r representing a signed integer number in a given conversion base.
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// It returns z, the actual conversion base used, and an error, if any. In the
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// error case, the value of z is undefined. The syntax follows the syntax of
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// integer literals in Go.
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//
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// The base argument must be 0 or a value from 2 through MaxBase. If the base
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// is 0, the string prefix determines the actual conversion base. A prefix of
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// ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
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// ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
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//
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func (z *Int) scan(r io.RuneScanner, base int) (*Int, int, os.Error) {
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// determine sign
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ch, _, err := r.ReadRune()
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if err != nil {
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return z, 0, err
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}
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neg := false
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switch ch {
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case '-':
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neg = true
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case '+': // nothing to do
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default:
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r.UnreadRune()
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}
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// determine mantissa
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z.abs, base, err = z.abs.scan(r, base)
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if err != nil {
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return z, base, err
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}
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z.neg = len(z.abs) > 0 && neg // 0 has no sign
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return z, base, nil
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}
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// Scan is a support routine for fmt.Scanner; it sets z to the value of
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// the scanned number. It accepts the formats 'b' (binary), 'o' (octal),
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// 'd' (decimal), 'x' (lowercase hexadecimal), and 'X' (uppercase hexadecimal).
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func (z *Int) Scan(s fmt.ScanState, ch int) os.Error {
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base := 0
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switch ch {
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case 'b':
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base = 2
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@ -394,32 +432,13 @@ func (x *Int) Scan(s fmt.ScanState, ch int) os.Error {
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default:
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return os.ErrorString("Int.Scan: invalid verb")
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}
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ch, _, err := s.ReadRune()
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if err != nil {
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_, _, err := z.scan(s, base)
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return err
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}
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neg := false
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switch ch {
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case '-':
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neg = true
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case '+': // nothing to do
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default:
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s.UnreadRune()
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}
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x.abs, _, err = x.abs.scan(s, base)
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if err != nil {
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return err
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}
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x.neg = len(x.abs) > 0 && neg // 0 has no sign
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return nil
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}
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// Int64 returns the int64 representation of z.
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// If z cannot be represented in an int64, the result is undefined.
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// Int64 returns the int64 representation of x.
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// If x cannot be represented in an int64, the result is undefined.
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func (x *Int) Int64() int64 {
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if len(x.abs) == 0 {
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return 0
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@ -439,32 +458,18 @@ func (x *Int) Int64() int64 {
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// and returns z and a boolean indicating success. If SetString fails,
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// the value of z is undefined.
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//
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// If the base argument is 0, the string prefix determines the actual
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// conversion base. A prefix of ``0x'' or ``0X'' selects base 16; the
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// ``0'' prefix selects base 8, and a ``0b'' or ``0B'' prefix selects
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// base 2. Otherwise the selected base is 10.
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// The base argument must be 0 or a value from 2 through MaxBase. If the base
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// is 0, the string prefix determines the actual conversion base. A prefix of
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// ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
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// ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
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//
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func (z *Int) SetString(s string, base int) (*Int, bool) {
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neg := false
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if len(s) > 0 {
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switch s[0] {
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case '-':
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neg = true
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fallthrough
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case '+':
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s = s[1:]
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}
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}
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r := strings.NewReader(s)
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abs, _, err := z.abs.scan(r, base)
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_, _, err := z.scan(r, base)
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if err != nil {
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return z, false
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}
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_, _, err = r.ReadRune()
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z.abs = abs
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z.neg = len(abs) > 0 && neg // 0 has no sign
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return z, err == os.EOF // err == os.EOF => scan consumed all of s
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}
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@ -608,8 +608,11 @@ func (x nat) bitLen() int {
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}
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func hexValue(ch int) int {
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var d int
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// MaxBase is the largest number base accepted for string conversions.
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const MaxBase = 'z' - 'a' + 10 + 1 // = hexValue('z') + 1
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func hexValue(ch int) Word {
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d := MaxBase + 1 // illegal base
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switch {
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case '0' <= ch && ch <= '9':
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d = ch - '0'
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@ -617,86 +620,106 @@ func hexValue(ch int) int {
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d = ch - 'a' + 10
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case 'A' <= ch && ch <= 'Z':
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d = ch - 'A' + 10
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default:
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return -1
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}
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return d
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return Word(d)
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}
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// scan returns the natural number corresponding to the longest
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// possible prefix read from r representing a natural number in a
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// given conversion base, the actual conversion base used, and an
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// error, if any. The syntax of natural numbers follows the syntax of
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// scan sets z to the natural number corresponding to the longest possible prefix
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// read from r representing an unsigned integer in a given conversion base.
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// It returns z, the actual conversion base used, and an error, if any. In the
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// error case, the value of z is undefined. The syntax follows the syntax of
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// unsigned integer literals in Go.
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//
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// If the base argument is 0, the string prefix determines the actual
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// conversion base. A prefix of ``0x'' or ``0X'' selects base 16; the
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// ``0'' prefix selects base 8, and a ``0b'' or ``0B'' prefix selects
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// base 2. Otherwise the selected base is 10.
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// The base argument must be 0 or a value from 2 through MaxBase. If the base
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// is 0, the string prefix determines the actual conversion base. A prefix of
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// ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
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// ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
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//
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func (z nat) scan(r io.RuneScanner, base int) (nat, int, os.Error) {
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n := 0
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// reject illegal bases
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if base < 0 || base == 1 || MaxBase < base {
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return z, 0, os.ErrorString("illegal number base")
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}
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// one char look-ahead
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ch, _, err := r.ReadRune()
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if err != nil {
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return z, 0, err
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}
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// determine base if necessary
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b := Word(base)
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if base == 0 {
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base = 10
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b = 10
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if ch == '0' {
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n++
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switch ch, _, err = r.ReadRune(); err {
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case nil:
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base = 8
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b = 8
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switch ch {
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case 'x', 'X':
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base = 16
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b = 16
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case 'b', 'B':
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base = 2
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b = 2
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}
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if base == 2 || base == 16 {
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n--
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if b == 2 || b == 16 {
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if ch, _, err = r.ReadRune(); err != nil {
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return z, 0, os.ErrorString("syntax error scanning binary or hexadecimal number")
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return z, 0, err
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}
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}
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case os.EOF:
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return z, 10, nil
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default:
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return z, 0, err
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return z, 10, err
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}
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}
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}
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// reject illegal bases
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if base < 2 || 'z'-'a'+10 < base {
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return z, 0, os.ErrorString("illegal number base")
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}
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// convert string
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// - group as many digits d as possible together into a "super-digit" dd with "super-base" bb
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// - only when bb does not fit into a word anymore, do a full number mulAddWW using bb and dd
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z = z.make(0)
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bb := Word(1)
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dd := Word(0)
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for {
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d := hexValue(ch)
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if 0 <= d && d < base {
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z = z.mulAddWW(z, Word(base), Word(d))
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if d >= b {
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r.UnreadRune() // ch does not belong to number anymore
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break
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}
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if tmp := bb * b; tmp < bb {
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// overflow
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z = z.mulAddWW(z, bb, dd)
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bb = b
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dd = d
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} else {
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r.UnreadRune()
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if n > 0 {
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break
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bb = tmp
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dd = dd*b + d
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}
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return z, 0, os.ErrorString("syntax error scanning number")
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}
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n++
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if ch, _, err = r.ReadRune(); err != nil {
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if err == os.EOF {
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break
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if err != os.EOF {
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return z, int(b), err
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}
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return z, 0, err
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break
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}
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}
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return z.norm(), base, nil
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switch {
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case bb > 1:
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// there was at least one mantissa digit
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z = z.mulAddWW(z, bb, dd)
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case base == 0 && b == 8:
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// there was only the octal prefix 0 (possibly followed by digits > 7);
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// return base 10, not 8
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return z, 10, nil
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case base != 0 || b != 8:
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// there was neither a mantissa digit nor the octal prefix 0
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return z, int(b), os.ErrorString("syntax error scanning number")
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}
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return z.norm(), int(b), nil
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}
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@ -5,6 +5,7 @@
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package big
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import (
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"os"
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"strings"
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"testing"
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)
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@ -211,28 +212,58 @@ func TestString(t *testing.T) {
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var natScanTests = []struct {
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s string // string to be scanned
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base int // input base
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x nat // expected nat
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base int // expected base
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b int // expected base
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ok bool // expected success
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next int // next character (or 0, if at EOF)
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}{
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{s: ""},
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{"0", nil, 10, true},
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{"0 ", nil, 8, true},
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// error: illegal base
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{base: -1},
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{base: 1},
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{base: 37},
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// error: no mantissa
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{},
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{s: "?"},
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{base: 10},
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{base: 36},
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{s: "?", base: 10},
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{s: "0x"},
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{"08", nil, 8, true},
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{"0b1", nat{1}, 2, true},
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{"0b11000101", nat{0xc5}, 2, true},
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{"03271", nat{03271}, 8, true},
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{"10ab", nat{10}, 10, true},
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{"1234567890", nat{1234567890}, 10, true},
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{"0xdeadbeef", nat{0xdeadbeef}, 16, true},
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{"0XDEADBEEF", nat{0xdeadbeef}, 16, true},
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{s: "345", base: 2},
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// no errors
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{"0", 0, nil, 10, true, 0},
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{"0", 10, nil, 10, true, 0},
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{"0", 36, nil, 36, true, 0},
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{"1", 0, nat{1}, 10, true, 0},
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{"1", 10, nat{1}, 10, true, 0},
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{"0 ", 0, nil, 10, true, ' '},
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{"08", 0, nil, 10, true, '8'},
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{"018", 0, nat{1}, 8, true, '8'},
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{"0b1", 0, nat{1}, 2, true, 0},
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{"0b11000101", 0, nat{0xc5}, 2, true, 0},
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{"03271", 0, nat{03271}, 8, true, 0},
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{"10ab", 0, nat{10}, 10, true, 'a'},
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{"1234567890", 0, nat{1234567890}, 10, true, 0},
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{"xyz", 36, nat{(33*36+34)*36 + 35}, 36, true, 0},
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{"xyz?", 36, nat{(33*36+34)*36 + 35}, 36, true, '?'},
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{"0x", 16, nil, 16, true, 'x'},
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{"0xdeadbeef", 0, nat{0xdeadbeef}, 16, true, 0},
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{"0XDEADBEEF", 0, nat{0xdeadbeef}, 16, true, 0},
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{"0xfedcba9876543213fedcba9876543212fedcba9876543211fedcba9876543210",
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0,
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nat{0xfedcba9876543210, 0xfedcba9876543211, 0xfedcba9876543212, 0xfedcba9876543213},
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16,
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true,
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0},
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}
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func TestScanBase0(t *testing.T) {
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func TestScanBase(t *testing.T) {
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for _, a := range natScanTests {
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x, b, err := nat(nil).scan(strings.NewReader(a.s), 0)
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r := strings.NewReader(a.s)
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x, b, err := nat(nil).scan(r, a.base)
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if err == nil && !a.ok {
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t.Errorf("scan%+v\n\texpected error", a)
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}
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@ -245,9 +276,92 @@ func TestScanBase0(t *testing.T) {
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if x.cmp(a.x) != 0 {
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t.Errorf("scan%+v\n\tgot z = %v; want %v", a, x, a.x)
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}
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if b != a.base {
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if b != a.b {
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t.Errorf("scan%+v\n\tgot b = %d; want %d", a, b, a.base)
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}
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next, _, err := r.ReadRune()
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if err == os.EOF {
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next = 0
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err = nil
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}
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if err == nil && next != a.next {
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t.Errorf("scan%+v\n\tgot next = %q; want %q", a, next, a.next)
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}
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}
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}
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var pi = "3" +
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"14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651" +
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"32823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461" +
|
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"28475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920" +
|
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"96282925409171536436789259036001133053054882046652138414695194151160943305727036575959195309218611738193261179" +
|
||||
"31051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798" +
|
||||
"60943702770539217176293176752384674818467669405132000568127145263560827785771342757789609173637178721468440901" +
|
||||
"22495343014654958537105079227968925892354201995611212902196086403441815981362977477130996051870721134999999837" +
|
||||
"29780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083" +
|
||||
"81420617177669147303598253490428755468731159562863882353787593751957781857780532171226806613001927876611195909" +
|
||||
"21642019893809525720106548586327886593615338182796823030195203530185296899577362259941389124972177528347913151" +
|
||||
"55748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240128583616035" +
|
||||
"63707660104710181942955596198946767837449448255379774726847104047534646208046684259069491293313677028989152104" +
|
||||
"75216205696602405803815019351125338243003558764024749647326391419927260426992279678235478163600934172164121992" +
|
||||
"45863150302861829745557067498385054945885869269956909272107975093029553211653449872027559602364806654991198818" +
|
||||
"34797753566369807426542527862551818417574672890977772793800081647060016145249192173217214772350141441973568548" +
|
||||
"16136115735255213347574184946843852332390739414333454776241686251898356948556209921922218427255025425688767179" +
|
||||
"04946016534668049886272327917860857843838279679766814541009538837863609506800642251252051173929848960841284886" +
|
||||
"26945604241965285022210661186306744278622039194945047123713786960956364371917287467764657573962413890865832645" +
|
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"99581339047802759009946576407895126946839835259570982582262052248940772671947826848260147699090264013639443745" +
|
||||
"53050682034962524517493996514314298091906592509372216964615157098583874105978859597729754989301617539284681382" +
|
||||
"68683868942774155991855925245953959431049972524680845987273644695848653836736222626099124608051243884390451244" +
|
||||
"13654976278079771569143599770012961608944169486855584840635342207222582848864815845602850601684273945226746767" +
|
||||
"88952521385225499546667278239864565961163548862305774564980355936345681743241125150760694794510965960940252288" +
|
||||
"79710893145669136867228748940560101503308617928680920874760917824938589009714909675985261365549781893129784821" +
|
||||
"68299894872265880485756401427047755513237964145152374623436454285844479526586782105114135473573952311342716610" +
|
||||
"21359695362314429524849371871101457654035902799344037420073105785390621983874478084784896833214457138687519435" +
|
||||
"06430218453191048481005370614680674919278191197939952061419663428754440643745123718192179998391015919561814675" +
|
||||
"14269123974894090718649423196156794520809514655022523160388193014209376213785595663893778708303906979207734672" +
|
||||
"21825625996615014215030680384477345492026054146659252014974428507325186660021324340881907104863317346496514539" +
|
||||
"05796268561005508106658796998163574736384052571459102897064140110971206280439039759515677157700420337869936007" +
|
||||
"23055876317635942187312514712053292819182618612586732157919841484882916447060957527069572209175671167229109816" +
|
||||
"90915280173506712748583222871835209353965725121083579151369882091444210067510334671103141267111369908658516398" +
|
||||
"31501970165151168517143765761835155650884909989859982387345528331635507647918535893226185489632132933089857064" +
|
||||
"20467525907091548141654985946163718027098199430992448895757128289059232332609729971208443357326548938239119325" +
|
||||
"97463667305836041428138830320382490375898524374417029132765618093773444030707469211201913020330380197621101100" +
|
||||
"44929321516084244485963766983895228684783123552658213144957685726243344189303968642624341077322697802807318915" +
|
||||
"44110104468232527162010526522721116603966655730925471105578537634668206531098965269186205647693125705863566201" +
|
||||
"85581007293606598764861179104533488503461136576867532494416680396265797877185560845529654126654085306143444318" +
|
||||
"58676975145661406800700237877659134401712749470420562230538994561314071127000407854733269939081454664645880797" +
|
||||
"27082668306343285878569830523580893306575740679545716377525420211495576158140025012622859413021647155097925923" +
|
||||
"09907965473761255176567513575178296664547791745011299614890304639947132962107340437518957359614589019389713111" +
|
||||
"79042978285647503203198691514028708085990480109412147221317947647772622414254854540332157185306142288137585043" +
|
||||
"06332175182979866223717215916077166925474873898665494945011465406284336639379003976926567214638530673609657120" +
|
||||
"91807638327166416274888800786925602902284721040317211860820419000422966171196377921337575114959501566049631862" +
|
||||
"94726547364252308177036751590673502350728354056704038674351362222477158915049530984448933309634087807693259939" +
|
||||
"78054193414473774418426312986080998886874132604721569516239658645730216315981931951673538129741677294786724229" +
|
||||
"24654366800980676928238280689964004824354037014163149658979409243237896907069779422362508221688957383798623001" +
|
||||
"59377647165122893578601588161755782973523344604281512627203734314653197777416031990665541876397929334419521541" +
|
||||
"34189948544473456738316249934191318148092777710386387734317720754565453220777092120190516609628049092636019759" +
|
||||
"88281613323166636528619326686336062735676303544776280350450777235547105859548702790814356240145171806246436267" +
|
||||
"94561275318134078330336254232783944975382437205835311477119926063813346776879695970309833913077109870408591337"
|
||||
|
||||
|
||||
// Test case for BenchmarkScanPi.
|
||||
func TestScanPi(t *testing.T) {
|
||||
var x nat
|
||||
z, _, err := x.scan(strings.NewReader(pi), 10)
|
||||
if err != nil {
|
||||
t.Errorf("scanning pi: %s", err)
|
||||
}
|
||||
if s := z.decimalString(); s != pi {
|
||||
t.Errorf("scanning pi: got %s", s)
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
func BenchmarkScanPi(b *testing.B) {
|
||||
for i := 0; i < b.N; i++ {
|
||||
var x nat
|
||||
x.scan(strings.NewReader(pi), 10)
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user