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https://github.com/golang/go
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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
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This test computes the precision of the compiler's internal multiprecision floats.
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package main
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import (
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"fmt"
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"math"
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"runtime"
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)
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const ulp = (1.0 + (2.0 / 3.0)) - (5.0 / 3.0)
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func main() {
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// adjust precision depending on compiler
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var prec float64
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switch runtime.Compiler {
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case "gc":
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prec = 512
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case "gccgo":
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prec = 256
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default:
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// unknown compiler
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return
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}
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p := 1 - math.Log(math.Abs(ulp))/math.Log(2)
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if math.Abs(p-prec) > 1e-10 {
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fmt.Printf("BUG: got %g; want %g\n", p, prec)
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}
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}
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