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5 Commits

Author SHA1 Message Date
Mohit Agarwal 7eed848a17 math: speed up Gamma(+Inf) 
Add special case for Gamma(+∞) which speeds it up:

benchmark            old ns/op     new ns/op     delta
BenchmarkGamma-4     14.5          7.44          -48.69%

The documentation for math.Gamma already specifies it as a special
case:

        Gamma(+Inf) = +Inf

The original C code that has been used as the reference implementation
(as mentioned in the comments in gamma.go) also treats Gamma(+∞) as a
special case:

if( x == INFINITY )
        return(x);

Change-Id: Idac36e19192b440475aec0796faa2d2c7f8abe0b
Reviewed-on: https://go-review.googlesource.com/31370
Reviewed-by: Robert Griesemer <gri@golang.org>
 2016-10-18 22:12:03 +00:00
Russ Cox 4f3a641e6e math: fix Gamma(-171.5) on all platforms 
Using 387 mode was computing it without underflow to zero,
apparently due to an 80-bit intermediate. Avoid underflow even
with 64-bit floats.

This eliminates the TODOs in the test suite.

Fixes linux-386-387 build and fixes #11441.

Change-Id: I8abaa63bfdf040438a95625d1cb61042f0302473
Reviewed-on: https://go-review.googlesource.com/30540
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
 2016-10-06 14:53:09 +00:00
Russ Cox a39920fdbb math: fix Gamma(x) for x < -170.5 and other corner cases 
Fixes #11441.

Test tables generated by

	package main

	import (
		"bytes"
		"fmt"
		"log"
		"os/exec"
		"strconv"
		"strings"
	)

	var inputs = []float64{
		0.5,
		1.5,
		2.5,
		3.5,
		-0.5,
		-1.5,
		-2.5,
		-3.5,
		0.1,
		0.01,
		1e-8,
		1e-16,
		1e-3,
		1e-16,
		1e-308,
		5.6e-309,
		5.5e-309,
		1e-309,
		1e-323,
		5e-324,
		-0.1,
		-0.01,
		-1e-8,
		-1e-16,
		-1e-3,
		-1e-16,
		-1e-308,
		-5.6e-309,
		-5.5e-309,
		-1e-300 / 1e9,
		-1e-300 / 1e23,
		-5e-300 / 1e24,
		-0.9999999999999999,
		-1.0000000000000002,
		-1.9999999999999998,
		-2.0000000000000004,
		-100.00000000000001,
		-99.999999999999986,
		17,
		171,
		171.6,
		171.624,
		171.625,
		172,
		2000,
		-100.5,
		-160.5,
		-170.5,
		-171.5,
		-176.5,
		-177.5,
		-178.5,
		-179.5,
		-201.0001,
		-202.9999,
		-1000.5,
		-1000000000.3,
		-4503599627370495.5,
		-63.349078729022985,
		-127.45117632943295,
	}

	func main() {
		var buf bytes.Buffer
		for _, v := range inputs {
			fmt.Fprintf(&buf, "gamma(%.1000g)\n", v)
		}
		cmd := exec.Command("gp", "-q")
		cmd.Stdin = &buf
		out, err := cmd.CombinedOutput()
		if err != nil {
			log.Fatalf("gp: %v", err)
		}
		f := strings.Split(string(out), "\n")
		if len(f) > 0 && f[len(f)-1] == "" {
			f = f[:len(f)-1]
		}
		if len(f) != len(inputs) {
			log.Fatalf("gp: wrong output count\n%s\n", out)
		}
		for i, g := range f {
			gf, err := strconv.ParseFloat(strings.Replace(g, " E", "e", -1), 64)
			if err != nil {
				if strings.Contains(err.Error(), "value out of range") {
					if strings.HasPrefix(g, "-") {
						fmt.Printf("\t{%g, Inf(-1)},\n", inputs[i])
					} else {
						fmt.Printf("\t{%g, Inf(1)},\n", inputs[i])
					}
					continue
				}
				log.Fatal(err)
			}
			if gf == 0 && strings.HasPrefix(g, "-") {
				fmt.Printf("\t{%g, Copysign(0, -1)},\n", inputs[i])
				continue
			}
			fmt.Printf("\t{%g, %g},\n", inputs[i], gf)
		}
	}

Change-Id: Ie98c7751d92b8ffb40e8313f5ea10df0890e2feb
Reviewed-on: https://go-review.googlesource.com/30146
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>
 2016-10-05 03:53:13 +00:00
Brad Fitzpatrick 5fea2ccc77 all: single space after period. 
The tree's pretty inconsistent about single space vs double space
after a period in documentation. Make it consistently a single space,
per earlier decisions. This means contributors won't be confused by
misleading precedence.

This CL doesn't use go/doc to parse. It only addresses // comments.
It was generated with:

$ perl -i -npe 's,^(\s*// .+[a-z]\.)  +([A-Z]),$1 $2,' $(git grep -l -E '^\s*//(.+\.)  +([A-Z])')
$ go test go/doc -update

Change-Id: Iccdb99c37c797ef1f804a94b22ba5ee4b500c4f7
Reviewed-on: https://go-review.googlesource.com/20022
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Dave Day <djd@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
 2016-03-02 00:13:47 +00:00
Russ Cox c007ce824d build: move package sources from src/pkg to src 
Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.
 2014-09-08 00:08:51 -04:00