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math: fix ternary correction statement in Log1p 

The original port of Log1p incorrectly translated a ternary statement
so that a correction was only applied to one of the branches.

Fixes #29488

Change-Id: I035b2fc741f76fe7c0154c63da6e298b575e08a4
Reviewed-on: https://go-review.googlesource.com/c/156120
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Brian Kessler 2019-01-03 10:00:49 -07:00 committed by Robert Griesemer
parent 55dec44010
commit 649294d0a5
2 changed files with 5 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/math/all_test.go
View File

@ -1528,6 +1528,7 @@ var vflog1pSC = []float64{
0,
Inf(1),
NaN(),
4503599627370496.5, // Issue #29488
}
var log1pSC = []float64{
NaN(),
@ -1537,6 +1538,7 @@ var log1pSC = []float64{
0,
Inf(1),
NaN(),
36.04365338911715, // Issue #29488
}
var vfmodfSC = []float64{

5
src/math/log1p.go
View File

@ -151,12 +151,13 @@ func log1p(x float64) float64 {
u = 1.0 + x
iu = Float64bits(u)
k = int((iu >> 52) - 1023)
// correction term
if k > 0 {
c = 1.0 - (u - x)
} else {
c = x - (u - 1.0) // correction term
c /= u
c = x - (u - 1.0)
}
c /= u
} else {
u = x
iu = Float64bits(u)