math/fixed: new package.

Fixes golang/go#11906

Change-Id: I2b43311ff145e8453cd255f085c82add6da7de5b
Reviewed-on: https://go-review.googlesource.com/12863
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Nigel Tao 2015-07-30 15:00:38 +10:00
parent 5f5d3e0618
commit 5ec5e003b2
2 changed files with 84 additions and 0 deletions

59
math/fixed/fixed.go Normal file
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// 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 fixed implements fixed-point integer types.
package fixed // import "golang.org/x/image/math/fixed"
import (
"fmt"
)
// TODO: implement fmt.Formatter for %f and %g.
// Int26_6 is a signed 26.6 fixed-point number.
//
// The integer part ranges from -33554432 to 33554431, inclusive. The
// fractional part has 6 bits of precision.
//
// For example, the number one-and-a-quarter is Int26_6(1<<6 + 1<<4).
type Int26_6 int32
// String returns a human-readable representation of a 26.6 fixed-point number.
//
// For example, the number one-and-a-quarter becomes "1:16".
func (x Int26_6) String() string {
const shift, mask = 6, 1<<6 - 1
if x >= 0 {
return fmt.Sprintf("%d:%02d", int32(x>>shift), int32(x&mask))
}
x = -x
if x >= 0 {
return fmt.Sprintf("-%d:%02d", int32(x>>shift), int32(x&mask))
}
return "-33554432:00" // The minimum value is -(1<<25).
}
// Int52_12 is a signed 52.12 fixed-point number.
//
// The integer part ranges from -2251799813685248 to 2251799813685247,
// inclusive. The fractional part has 12 bits of precision.
//
// For example, the number one-and-a-quarter is Int52_12(1<<12 + 1<<10).
type Int52_12 int64
// String returns a human-readable representation of a 52.12 fixed-point
// number.
//
// For example, the number one-and-a-quarter becomes "1:1024".
func (x Int52_12) String() string {
const shift, mask = 12, 1<<12 - 1
if x >= 0 {
return fmt.Sprintf("%d:%04d", int64(x>>shift), int64(x&mask))
}
x = -x
if x >= 0 {
return fmt.Sprintf("-%d:%04d", int64(x>>shift), int64(x&mask))
}
return "-2251799813685248:0000" // The minimum value is -(1<<51).
}

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math/fixed/fixed_test.go Normal file
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// 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 fixed
import (
"testing"
)
func TestInt26_6(t *testing.T) {
got := Int26_6(1<<6 + 1<<4).String()
want := "1:16"
if got != want {
t.Fatalf("got %q, want %q", got, want)
}
}
func TestInt52_12(t *testing.T) {
got := Int52_12(1<<12 + 1<<10).String()
want := "1:1024"
if got != want {
t.Fatalf("got %q, want %q", got, want)
}
}