mirror of
https://github.com/golang/go
synced 2024-11-24 21:40:09 -07:00
a51d5f27e8
The original implementation used 16 int "words" but only 29 bits per word for a total of 16*29 = 464 bits, with a space consumption of 16*64 = 1024 bits on a 64 bit machine. Switching to 512 bits increases precision while still using (in the worst case) half the amount of memory per mp value on a 64 bit machine. Also: Decreased permitted number of least-significant mantissa bits which may be incorrect when considering if a precise floating-point constant is an integer from 29 to 16 bits. Change-Id: Iee9287056f0e9aa4f06ceac0724ff4674f710c53 Reviewed-on: https://go-review.googlesource.com/8429 Reviewed-by: Russ Cox <rsc@golang.org>
36 lines
683 B
Go
36 lines
683 B
Go
// run
|
|
|
|
// 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.
|
|
|
|
// This test computes the precision of the compiler's internal multiprecision floats.
|
|
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"math"
|
|
"runtime"
|
|
)
|
|
|
|
const ulp = (1.0 + (2.0 / 3.0)) - (5.0 / 3.0)
|
|
|
|
func main() {
|
|
// adjust precision depending on compiler
|
|
var prec float64
|
|
switch runtime.Compiler {
|
|
case "gc":
|
|
prec = 512
|
|
case "gccgo":
|
|
prec = 256
|
|
default:
|
|
// unknown compiler
|
|
return
|
|
}
|
|
p := 1 - math.Log(math.Abs(ulp))/math.Log(2)
|
|
if math.Abs(p-prec) > 1e-10 {
|
|
fmt.Printf("BUG: got %g; want %g\n", p, prec)
|
|
}
|
|
}
|