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math/big: remove Float.Lsh/Rsh; added shift example

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Shifts are trivially implemented by combining
Float.MantExp and Float.SetMantExp.

Change-Id: Ia2fb49297d8ea7aa7d64c8b1318dc3dc7c8af2f7
Reviewed-on: https://go-review.googlesource.com/6671
Reviewed-by: Alan Donovan <adonovan@google.com>
This commit is contained in:
Robert Griesemer 2015-03-03 12:53:41 -08:00
parent d934d10a0b
commit ef0b03137d
2 changed files with 36 additions and 40 deletions
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44
src/math/big/float.go
View File

@ -88,8 +88,8 @@ const (
// Accuracy describes the rounding error produced by the most recent
// operation that generated a Float value, relative to the exact value.
// The accuracy may be Undef (either Below or Above) for operations on
// and resulting in NaNs.
// The accuracy may be Undef for operations on and resulting in
// NaNs since they are neither Below nor Above any other value.
type Accuracy int8
// Constants describing the Accuracy of a Float.
@ -278,6 +278,8 @@ func (x *Float) MantExp(mant *Float) (exp int) {
// z.SetMantExp(±Inf, exp) = ±Inf
// z.SetMantExp( NaN, exp) = NaN
//
// z and mant may be the same in which case z's exponent
// is set to exp.
func (z *Float) SetMantExp(mant *Float, exp int) *Float {
if debugFloat {
validate(z)
@ -1449,44 +1451,6 @@ func (z *Float) Quo(x, y *Float) *Float {
return z
}
// TODO(gri) eliminate Lsh, Rsh? We can do the same with MantExp, SetMantExp.
// Lsh sets z to the rounded x * (1<<s) and returns z.
// If z's precision is 0, it is changed to x's precision.
// Rounding is performed according to z's precision
// and rounding mode; and z's accuracy reports the
// result error relative to the exact (not rounded)
// result.
// BUG(gri) Lsh is not tested and may not work correctly.
func (z *Float) Lsh(x *Float, s uint) *Float {
if debugFloat {
validate(x)
}
z.Set(x)
if len(x.mant) != 0 {
z.setExp(int64(z.exp) + int64(s))
}
return z
}
// Rsh sets z to the rounded x / (1<<s) and returns z.
// Precision, rounding, and accuracy reporting are as for Lsh.
// BUG(gri) Rsh is not tested and may not work correctly.
func (z *Float) Rsh(x *Float, s uint) *Float {
if debugFloat {
validate(x)
}
z.Set(x)
if len(x.mant) != 0 {
z.setExp(int64(z.exp) - int64(s))
}
return z
}
// Cmp compares x and y and returns:
//
// -1 if x < y

32
src/math/big/floatexample_test.go Normal file
View File

@ -0,0 +1,32 @@
// Copyright 2015 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.
package big_test
import (
"fmt"
"math/big"
)
func Example_Shift() {
// Implementing Float "shift" by modifying the (binary) exponents directly.
var x big.Float
for s := -5; s <= 5; s++ {
x.SetFloat64(0.5)
x.SetMantExp(&x, x.MantExp(nil)+s) // shift x by s
fmt.Println(&x)
}
// Output:
// 0.015625
// 0.03125
// 0.0625
// 0.125
// 0.25
// 0.5
// 1
// 2
// 4
// 8
// 16
}