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big: implemented Karatsuba multiplication

Browse Source 
Plus:
- calibration "test" - include in tests with gotest -calibrate
- basic Mul benchmark
- extra multiplication tests
- various cleanups

This change improves multiplication speed of numbers >= 30 words
in length (current threshold; found empirically with calibrate):

The multiplication benchmark (multiplication of a variety of long numbers)
improves by ~35%, individual multiplies can be significantly faster.

gotest -benchmarks=Mul
big.BenchmarkMul	     500	   6829290 ns/op (w/ Karatsuba)
big.BenchmarkMul	     100	  10600760 ns/op

There's no impact on pidigits for -n=10000 or -n=20000
because the operands are are too small.

R=rsc
CC=golang-dev
https://golang.org/cl/1004042
This commit is contained in:
Robert Griesemer 2010-04-27 19:16:08 -07:00
parent dc606a20ce
commit b2183701c0
5 changed files with 496 additions and 97 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

91
src/pkg/big/calibrate_test.go Normal file
View File

@ -0,0 +1,91 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file computes the Karatsuba threshold as a "test".
// Usage: gotest -calibrate
package big
import (
"flag"
"fmt"
"testing"
"time"
"unsafe" // for Sizeof
)
var calibrate = flag.Bool("calibrate", false, "run calibration test")
// makeNumber creates an n-word number 0xffff...ffff
func makeNumber(n int) *Int {
var w Word
b := make([]byte, n*unsafe.Sizeof(w))
for i := range b {
b[i] = 0xff
}
var x Int
x.SetBytes(b)
return &x
}
// measure returns the time to compute x*x in nanoseconds
func measure(f func()) int64 {
const N = 100
start := time.Nanoseconds()
for i := N; i > 0; i-- {
f()
}
stop := time.Nanoseconds()
return (stop - start) / N
}
func computeThreshold(t *testing.T) int {
// use a mix of numbers as work load
x := make([]*Int, 20)
for i := range x {
x[i] = makeNumber(10 * (i + 1))
}
threshold := -1
for n := 8; threshold < 0 || n <= threshold+20; n += 2 {
// set work load
f := func() {
var t Int
for _, x := range x {
t.Mul(x, x)
}
}
karatsubaThreshold = 1e9 // disable karatsuba
t1 := measure(f)
karatsubaThreshold = n // enable karatsuba
t2 := measure(f)
c := '<'
mark := ""
if t1 > t2 {
c = '>'
if threshold < 0 {
threshold = n
mark = " *"
}
}
fmt.Printf("%4d: %8d %c %8d%s\n", n, t1, c, t2, mark)
}
return threshold
}
func TestCalibrate(t *testing.T) {
if *calibrate {
fmt.Printf("Computing Karatsuba threshold\n")
fmt.Printf("threshold = %d\n", computeThreshold(t))
}
}

6
src/pkg/big/int.go
View File

@ -230,7 +230,7 @@ Error:
// sets z to that value.
func (z *Int) SetBytes(b []byte) *Int {
s := int(_S)
z.abs = z.abs.make((len(b)+s-1)/s, false)
z.abs = z.abs.make((len(b) + s - 1) / s)
z.neg = false
j := 0
@ -386,7 +386,7 @@ func ProbablyPrime(z *Int, n int) bool { return !z.neg && z.abs.probablyPrime(n)
func (z *Int) Lsh(x *Int, n uint) *Int {
addedWords := int(n) / _W
// Don't assign z.abs yet, in case z == x
znew := z.abs.make(len(x.abs)+addedWords+1, false)
znew := z.abs.make(len(x.abs) + addedWords + 1)
z.neg = x.neg
znew[addedWords:].shiftLeft(x.abs, n%_W)
for i := range znew[0:addedWords] {
@ -401,7 +401,7 @@ func (z *Int) Lsh(x *Int, n uint) *Int {
func (z *Int) Rsh(x *Int, n uint) *Int {
removedWords := int(n) / _W
// Don't assign z.abs yet, in case z == x
znew := z.abs.make(len(x.abs)-removedWords, false)
znew := z.abs.make(len(x.abs) - removedWords)
z.neg = x.neg
znew.shiftRight(x.abs[removedWords:], n%_W)
z.abs = znew.norm()

85
src/pkg/big/int_test.go
View File

@ -93,36 +93,55 @@ func TestProdZZ(t *testing.T) {
}
var facts = map[int]string{
0: "1",
1: "1",
2: "2",
10: "3628800",
20: "2432902008176640000",
100: "933262154439441526816992388562667004907159682643816214685929" +
"638952175999932299156089414639761565182862536979208272237582" +
"51185210916864000000000000000000000000",
}
// mulBytes returns x*y via grade school multiplication. Both inputs
// and the result are assumed to be in big-endian representation (to
// match the semantics of Int.Bytes and Int.SetBytes).
func mulBytes(x, y []byte) []byte {
z := make([]byte, len(x)+len(y))
func fact(n int) *Int {
var z Int
z.New(1)
for i := 2; i <= n; i++ {
var t Int
t.New(int64(i))
z.Mul(&z, &t)
}
return &z
}
func TestFact(t *testing.T) {
for n, s := range facts {
f := fact(n).String()
if f != s {
t.Errorf("%d! = %s; want %s", n, f, s)
// multiply
k0 := len(z) - 1
for j := len(y) - 1; j >= 0; j-- {
d := int(y[j])
if d != 0 {
k := k0
carry := 0
for i := len(x) - 1; i >= 0; i-- {
t := int(z[k]) + int(x[i])*d + carry
z[k], carry = byte(t), t>>8
k--
}
z[k] = byte(carry)
}
k0--
}
// normalize (remove leading 0's)
i := 0
for i < len(z) && z[i] == 0 {
i++
}
return z[i:]
}
func checkMul(a, b []byte) bool {
var x, y, z1 Int
x.SetBytes(a)
y.SetBytes(b)
z1.Mul(&x, &y)
var z2 Int
z2.SetBytes(mulBytes(a, b))
return z1.Cmp(&z2) == 0
}
func TestMul(t *testing.T) {
if err := quick.Check(checkMul, nil); err != nil {
t.Error(err)
}
}
@ -235,8 +254,7 @@ func checkSetBytes(b []byte) bool {
func TestSetBytes(t *testing.T) {
err := quick.Check(checkSetBytes, nil)
if err != nil {
if err := quick.Check(checkSetBytes, nil); err != nil {
t.Error(err)
}
}
@ -249,8 +267,7 @@ func checkBytes(b []byte) bool {
func TestBytes(t *testing.T) {
err := quick.Check(checkSetBytes, nil)
if err != nil {
if err := quick.Check(checkSetBytes, nil); err != nil {
t.Error(err)
}
}
@ -302,8 +319,7 @@ var divTests = []divTest{
func TestDiv(t *testing.T) {
err := quick.Check(checkDiv, nil)
if err != nil {
if err := quick.Check(checkDiv, nil); err != nil {
t.Error(err)
}
@ -676,6 +692,7 @@ var int64Tests = []int64{
-9223372036854775808,
}
func TestInt64(t *testing.T) {
for i, testVal := range int64Tests {
in := NewInt(testVal)

353
src/pkg/big/nat.go
View File

@ -36,6 +36,20 @@ import "rand"
type nat []Word
var (
natOne = nat{1}
natTwo = nat{2}
)
func (z nat) clear() nat {
for i := range z {
z[i] = 0
}
return z
}
func (z nat) norm() nat {
i := len(z)
for i > 0 && z[i-1] == 0 {
@ -46,15 +60,9 @@ func (z nat) norm() nat {
}
func (z nat) make(m int, clear bool) nat {
func (z nat) make(m int) nat {
if cap(z) > m {
z = z[0:m] // reuse z - has at least one extra word for a carry, if any
if clear {
for i := range z {
z[i] = 0
}
}
return z
return z[0:m] // reuse z - has at least one extra word for a carry, if any
}
c := 4 // minimum capacity
@ -67,12 +75,12 @@ func (z nat) make(m int, clear bool) nat {
func (z nat) new(x uint64) nat {
if x == 0 {
return z.make(0, false)
return z.make(0)
}
// single-digit values
if x == uint64(Word(x)) {
z = z.make(1, false)
z = z.make(1)
z[0] = Word(x)
return z
}
@ -84,7 +92,7 @@ func (z nat) new(x uint64) nat {
}
// split x into n words
z = z.make(n, false)
z = z.make(n)
for i := 0; i < n; i++ {
z[i] = Word(x & _M)
x >>= _W
@ -95,7 +103,7 @@ func (z nat) new(x uint64) nat {
func (z nat) set(x nat) nat {
z = z.make(len(x), false)
z = z.make(len(x))
for i, d := range x {
z[i] = d
}
@ -112,14 +120,14 @@ func (z nat) add(x, y nat) nat {
return z.add(y, x)
case m == 0:
// n == 0 because m >= n; result is 0
return z.make(0, false)
return z.make(0)
case n == 0:
// result is x
return z.set(x)
}
// m > 0
z = z.make(m, false)
z = z.make(m)
c := addVV(&z[0], &x[0], &y[0], n)
if m > n {
c = addVW(&z[n], &x[n], c, m-n)
@ -142,14 +150,14 @@ func (z nat) sub(x, y nat) nat {
panic("underflow")
case m == 0:
// n == 0 because m >= n; result is 0
return z.make(0, false)
return z.make(0)
case n == 0:
// result is x
return z.set(x)
}
// m > 0
z = z.make(m, false)
z = z.make(m)
c := subVV(&z[0], &x[0], &y[0], n)
if m > n {
c = subVW(&z[n], &x[n], c, m-n)
@ -198,7 +206,7 @@ func (z nat) mulAddWW(x nat, y, r Word) nat {
}
// m > 0
z = z.make(m, false)
z = z.make(m)
c := mulAddVWW(&z[0], &x[0], y, r, m)
if c > 0 {
z = z[0 : m+1]
@ -209,6 +217,173 @@ func (z nat) mulAddWW(x nat, y, r Word) nat {
}
// basicMul multiplies x and y and leaves the result in z.
// The (non-normalized) result is placed in z[0 : len(x) + len(y)].
func basicMul(z, x, y nat) {
// initialize z
for i := range z[0 : len(x)+len(y)] {
z[i] = 0
}
// multiply
for i, d := range y {
if d != 0 {
z[len(x)+i] = addMulVVW(&z[i], &x[0], d, len(x))
}
}
}
// Fast version of z[0:n+n>>1].add(z[0:n+n>>1], x[0:n]) w/o bounds checks.
// Factored out for readability - do not use outside karatsuba.
func karatsubaAdd(z, x nat, n int) {
if c := addVV(&z[0], &z[0], &x[0], n); c != 0 {
addVW(&z[n], &z[n], c, n>>1)
}
}
// Like karatsubaAdd, but does subtract.
func karatsubaSub(z, x nat, n int) {
if c := subVV(&z[0], &z[0], &x[0], n); c != 0 {
subVW(&z[n], &z[n], c, n>>1)
}
}
// Operands that are shorter than karatsubaThreshold are multiplied using
// "grade school" multiplication; for longer operands the Karatsuba algorithm
// is used.
var karatsubaThreshold int = 30 // modified by calibrate.go
// karatsuba multiplies x and y and leaves the result in z.
// Both x and y must have the same length n and n must be a
// power of 2. The result vector z must have len(z) >= 6*n.
// The (non-normalized) result is placed in z[0 : 2*n].
func karatsuba(z, x, y nat) {
n := len(y)
// Switch to basic multiplication if numbers are odd or small.
// (n is always even if karatsubaThreshold is even, but be
// conservative)
if n&1 != 0 || n < karatsubaThreshold || n < 2 {
basicMul(z, x, y)
return
}
// n&1 == 0 && n >= karatsubaThreshold && n >= 2
// Karatsuba multiplication is based on the observation that
// for two numbers x and y with:
//
// x = x1*b + x0
// y = y1*b + y0
//
// the product x*y can be obtained with 3 products z2, z1, z0
// instead of 4:
//
// x*y = x1*y1*b*b + (x1*y0 + x0*y1)*b + x0*y0
// = z2*b*b + z1*b + z0
//
// with:
//
// xd = x1 - x0
// yd = y0 - y1
//
// z1 = xd*yd + z1 + z0
// = (x1-x0)*(y0 - y1) + z1 + z0
// = x1*y0 - x1*y1 - x0*y0 + x0*y1 + z1 + z0
// = x1*y0 - z1 - z0 + x0*y1 + z1 + z0
// = x1*y0 + x0*y1
// split x, y into "digits"
n2 := n >> 1 // n2 >= 1
x1, x0 := x[n2:], x[0:n2] // x = x1*b + y0
y1, y0 := y[n2:], y[0:n2] // y = y1*b + y0
// z is used for the result and temporary storage:
//
// 6*n 5*n 4*n 3*n 2*n 1*n 0*n
// z = [z2 copy|z0 copy| xd*yd | yd:xd | x1*y1 | x0*y0 ]
//
// For each recursive call of karatsuba, an unused slice of
// z is passed in that has (at least) half the length of the
// caller's z.
// compute z0 and z2 with the result "in place" in z
karatsuba(z, x0, y0) // z0 = x0*y0
karatsuba(z[n:], x1, y1) // z2 = x1*y1
// compute xd (or the negative value if underflow occurs)
s := 1 // sign of product xd*yd
xd := z[2*n : 2*n+n2]
if subVV(&xd[0], &x1[0], &x0[0], n2) != 0 { // x1-x0
s = -s
subVV(&xd[0], &x0[0], &x1[0], n2) // x0-x1
}
// compute yd (or the negative value if underflow occurs)
yd := z[2*n+n2 : 3*n]
if subVV(&yd[0], &y0[0], &y1[0], n2) != 0 { // y0-y1
s = -s
subVV(&yd[0], &y1[0], &y0[0], n2) // y1-y0
}
// p = (x1-x0)*(y0-y1) == x1*y0 - x1*y1 - x0*y0 + x0*y1 for s > 0
// p = (x0-x1)*(y0-y1) == x0*y0 - x0*y1 - x1*y0 + x1*y1 for s < 0
p := z[n*3:]
karatsuba(p, xd, yd)
// save original z2:z0
// (ok to use upper half of z since we're done recursing)
r := z[n*4:]
copy(r, z)
// add up all partial products
//
// 2*n n 0
// z = [ z2 | z0 ]
// + [ z0 ]
// + [ z2 ]
// + [ p ]
//
karatsubaAdd(z[n2:], r, n)
karatsubaAdd(z[n2:], r[n:], n)
if s > 0 {
karatsubaAdd(z[n2:], p, n)
} else {
karatsubaSub(z[n2:], p, n)
}
}
// alias returns true if x and y share the same base array.
func alias(x, y nat) bool {
return &x[0:cap(x)][cap(x)-1] == &y[0:cap(y)][cap(y)-1]
}
// addAt implements z += x*(1<<(_W*i)); z must be long enough.
// (we don't use nat.add because we need z to stay the same
// slice, and we don't need to normalize z after each addition)
func addAt(z, x nat, i int) {
if n := len(x); n > 0 {
if c := addVV(&z[i], &z[i], &x[0], n); c != 0 {
j := i + n
if j < len(z) {
addVW(&z[j], &z[j], c, len(z)-j)
}
}
}
}
func max(x, y int) int {
if x > y {
return x
}
return y
}
func (z nat) mul(x, y nat) nat {
m := len(x)
n := len(y)
@ -217,25 +392,86 @@ func (z nat) mul(x, y nat) nat {
case m < n:
return z.mul(y, x)
case m == 0 || n == 0:
return z.make(0, false)
return z.make(0)
case n == 1:
return z.mulAddWW(x, y[0], 0)
}
// m >= n && m > 1 && n > 1
// m >= n > 1
if z == nil || &z[0] == &x[0] || &z[0] == &y[0] {
z = nat(nil).make(m+n, true) // z is an alias for x or y - cannot reuse
} else {
z = z.make(m+n, true)
// determine if z can be reused
if len(z) > 0 && (alias(z, x) || alias(z, y)) {
z = nil // z is an alias for x or y - cannot reuse
}
for i := 0; i < n; i++ {
if f := y[i]; f != 0 {
z[m+i] = addMulVVW(&z[i], &x[0], f, m)
}
}
z = z.norm()
return z
// use basic multiplication if the numbers are small
if n < karatsubaThreshold || n < 2 {
z = z.make(m + n)
basicMul(z, x, y)
return z.norm()
}
// m >= n && n >= karatsubaThreshold && n >= 2
// determine largest k such that
//
// x = x1*b + x0
// y = y1*b + y0 (and k <= len(y), which implies k <= len(x))
// b = 1<<(_W*k) ("base" of digits xi, yi)
//
// and k is karatsubaThreshold multiplied by a power of 2
k := max(karatsubaThreshold, 2)
for k*2 <= n {
k *= 2
}
// k <= n
// multiply x0 and y0 via Karatsuba
x0 := x[0:k] // x0 is not normalized
y0 := y[0:k] // y0 is not normalized
z = z.make(max(6*k, m+n)) // enough space for karatsuba of x0*y0 and full result of x*y
karatsuba(z, x0, y0)
z = z[0 : m+n] // z has final length but may be incomplete, upper portion is garbage
// If x1 and/or y1 are not 0, add missing terms to z explicitly:
//
// m+n 2*k 0
// z = [ ... | x0*y0 ]
// + [ x1*y1 ]
// + [ x1*y0 ]
// + [ x0*y1 ]
//
if k < n || m != n {
x1 := x[k:] // x1 is normalized because x is
y1 := y[k:] // y1 is normalized because y is
var t nat
t = t.mul(x1, y1)
copy(z[2*k:], t)
z[2*k+len(t):].clear() // upper portion of z is garbage
t = t.mul(x1, y0.norm())
addAt(z, t, k)
t = t.mul(x0.norm(), y1)
addAt(z, t, k)
}
return z.norm()
}
// mulRange computes the product of all the unsigned integers in the
// range [a, b] inclusively. If a > b (empty range), the result is 1.
func (z nat) mulRange(a, b uint64) nat {
switch {
case a == 0:
// cut long ranges short (optimization)
return z.new(0)
case a > b:
return z.new(1)
case a == b:
return z.new(a)
case a+1 == b:
return z.mul(nat(nil).new(a), nat(nil).new(b))
}
m := (a + b) / 2
return z.mul(nat(nil).mulRange(a, m), nat(nil).mulRange(m+1, b))
}
@ -253,7 +489,7 @@ func (z nat) divW(x nat, y Word) (q nat, r Word) {
return
}
// m > 0
z = z.make(m, false)
z = z.make(m)
r = divWVW(&z[0], 0, &x[0], y, m)
q = z.norm()
return
@ -266,7 +502,7 @@ func (z nat) div(z2, u, v nat) (q, r nat) {
}
if u.cmp(v) < 0 {
q = z.make(0, false)
q = z.make(0)
r = z2.set(u)
return
}
@ -275,10 +511,10 @@ func (z nat) div(z2, u, v nat) (q, r nat) {
var rprime Word
q, rprime = z.divW(u, v[0])
if rprime > 0 {
r = z2.make(1, false)
r = z2.make(1)
r[0] = rprime
} else {
r = z2.make(0, false)
r = z2.make(0)
}
return
}
@ -299,12 +535,12 @@ func (z nat) divLarge(z2, uIn, v nat) (q, r nat) {
var u nat
if z2 == nil || &z2[0] == &uIn[0] {
u = u.make(len(uIn)+1, true) // uIn is an alias for z2
u = u.make(len(uIn) + 1).clear() // uIn is an alias for z2
} else {
u = z2.make(len(uIn)+1, true)
u = z2.make(len(uIn) + 1).clear()
}
qhatv := make(nat, len(v)+1)
q = z.make(m+1, false)
q = z.make(m + 1)
// D1.
shift := uint(leadingZeroBits(v[n-1]))
@ -363,11 +599,11 @@ func (z nat) divLarge(z2, uIn, v nat) (q, r nat) {
// The result is the integer n for which 2^n <= x < 2^(n+1).
// If x == 0, the result is -1.
func log2(x Word) int {
n := 0
n := -1
for ; x > 0; x >>= 1 {
n++
}
return n - 1
return n
}
@ -375,9 +611,8 @@ func log2(x Word) int {
// The result is the integer n for which 2^n <= x < 2^(n+1).
// If x == 0, the result is -1.
func (x nat) log2() int {
m := len(x)
if m > 0 {
return (m-1)*_W + log2(x[m-1])
if i := len(x) - 1; i >= 0 {
return i*_W + log2(x[i])
}
return -1
}
@ -535,6 +770,9 @@ func trailingZeroBits(x Word) int {
}
// TODO(gri) Make the shift routines faster.
// Use pidigits.go benchmark as a test case.
// To avoid losing the top n bits, z should be sized so that
// len(z) == len(x) + 1.
func (z nat) shiftLeft(x nat, n uint) nat {
@ -582,7 +820,7 @@ func greaterThan(x1, x2, y1, y2 Word) bool { return x1 > y1 || x1 == y1 && x2 >
func (x nat) modW(d Word) (r Word) {
// TODO(agl): we don't actually need to store the q value.
var q nat
q = q.make(len(x), false)
q = q.make(len(x))
return divWVW(&q[0], 0, &x[0], d, len(x))
}
@ -601,7 +839,7 @@ func (n nat) powersOfTwoDecompose() (q nat, k Word) {
// zeroWords < len(n).
x := trailingZeroBits(n[zeroWords])
q = q.make(len(n)-zeroWords, false)
q = q.make(len(n) - zeroWords)
q.shiftRight(n[zeroWords:], uint(x))
q = q.norm()
@ -618,7 +856,7 @@ func (z nat) random(rand *rand.Rand, limit nat, n int) nat {
bitLengthOfMSW = _W
}
mask := Word((1 << bitLengthOfMSW) - 1)
z = z.make(len(limit), false)
z = z.make(len(limit))
for {
for i := range z {
@ -645,14 +883,14 @@ func (z nat) random(rand *rand.Rand, limit nat, n int) nat {
// reuses the storage of z if possible.
func (z nat) expNN(x, y, m nat) nat {
if len(y) == 0 {
z = z.make(1, false)
z = z.make(1)
z[0] = 1
return z
}
if m != nil {
// We likely end up being as long as the modulus.
z = z.make(len(m), false)
z = z.make(len(m))
}
z = z.set(x)
v := y[len(y)-1]
@ -715,14 +953,6 @@ func (z nat) len() int {
}
const (
primesProduct32 = 0xC0CFD797 // Π {p ∈ primes, 2 < p <= 29}
primesProduct64 = 0xE221F97C30E94E1D // Π {p ∈ primes, 2 < p <= 53}
)
var bigOne = nat{1}
var bigTwo = nat{2}
// probablyPrime performs reps Miller-Rabin tests to check whether n is prime.
// If it returns true, n is prime with probability 1 - 1/4^reps.
// If it returns false, n is not prime.
@ -750,6 +980,9 @@ func (n nat) probablyPrime(reps int) bool {
}
}
const primesProduct32 = 0xC0CFD797 // Π {p ∈ primes, 2 < p <= 29}
const primesProduct64 = 0xE221F97C30E94E1D // Π {p ∈ primes, 2 < p <= 53}
var r Word
switch _W {
case 32:
@ -770,11 +1003,11 @@ func (n nat) probablyPrime(reps int) bool {
return false
}
nm1 := nat(nil).sub(n, bigOne)
nm1 := nat(nil).sub(n, natOne)
// 1<<k * q = nm1;
q, k := nm1.powersOfTwoDecompose()
nm3 := nat(nil).sub(nm1, bigTwo)
nm3 := nat(nil).sub(nm1, natTwo)
rand := rand.New(rand.NewSource(int64(n[0])))
var x, y, quotient nat
@ -783,9 +1016,9 @@ func (n nat) probablyPrime(reps int) bool {
NextRandom:
for i := 0; i < reps; i++ {
x = x.random(rand, nm3, nm3Len)
x = x.add(x, bigTwo)
x = x.add(x, natTwo)
y = y.expNN(x, q, n)
if y.cmp(bigOne) == 0 || y.cmp(nm1) == 0 {
if y.cmp(natOne) == 0 || y.cmp(nm1) == 0 {
continue
}
for j := Word(1); j < k; j++ {
@ -794,7 +1027,7 @@ NextRandom:
if y.cmp(nm1) == 0 {
continue NextRandom
}
if y.cmp(bigOne) == 0 {
if y.cmp(natOne) == 0 {
return false
}
}

58
src/pkg/big/nat_test.go
View File

@ -111,6 +111,64 @@ func TestFunNN(t *testing.T) {
}
type mulRange struct {
a, b uint64
prod string
}
var mulRanges = []mulRange{
mulRange{0, 0, "0"},
mulRange{1, 1, "1"},
mulRange{1, 2, "2"},
mulRange{1, 3, "6"},
mulRange{1, 3, "6"},
mulRange{10, 10, "10"},
mulRange{0, 100, "0"},
mulRange{0, 1e9, "0"},
mulRange{100, 1, "1"}, // empty range
mulRange{1, 10, "3628800"}, // 10!
mulRange{1, 20, "2432902008176640000"}, // 20!
mulRange{1, 100,
"933262154439441526816992388562667004907159682643816214685929" +
"638952175999932299156089414639761565182862536979208272237582" +
"51185210916864000000000000000000000000", // 100!
},
}
func TestMulRange(t *testing.T) {
for i, r := range mulRanges {
prod := nat(nil).mulRange(r.a, r.b).string(10)
if prod != r.prod {
t.Errorf("%d: got %s; want %s", i, prod, r.prod)
}
}
}
var mulArg nat
func init() {
const n = 1000
mulArg = make(nat, n)
for i := 0; i < n; i++ {
mulArg[i] = _M
}
}
func BenchmarkMul(b *testing.B) {
for i := 0; i < b.N; i++ {
var t nat
for j := 1; j <= 10; j++ {
x := mulArg[0 : j*100]
t.mul(x, x)
}
}
}
type strN struct {
x nat
b int