From: "Stefan Kanthak" <stefan.kanthak@nexgo.de>
To: <musl@lists.openwall.com>
Subject: [musl] [PATCH] Properly simplified nextafter()
Date: Tue, 10 Aug 2021 08:23:46 +0200 [thread overview]
Message-ID: <0C6AAAD55DA44C6189B2FF4F5FB2C3E7@H270> (raw)
[-- Attachment #1: Type: text/plain, Size: 1426 bytes --]
<https://git.musl-libc.org/cgit/musl/plain/src/math/nextafter.c>
has quite some superfluous statements:
1. there's absolutely no need for 2 uint64_t holding |x| and |y|;
2. IEEE-754 specifies -0.0 == +0.0, so (x == y) is equivalent to
(ax == 0) && (ay == 0): the latter 2 tests can be removed;
3. there's absolutely no need to compare the signs of x and y
with the sign of the direction: its sufficient to test that
direction and sign of x match;
4. a proper compiler/optimizer should be able to reuse the results
of the comparision (x == y) for (x < y) or (x > y) and
(x == 0.0) for (x < 0.0) or (x > 0.0).
JFTR: if ((x < 0.0) == (x < y)) is equivalent to
if ((x > 0.0) == (x > y))
--- -/src/math/nextafter.c
+++ +/src/math/nextafter.c
@@ -3,20 +3,15 @@
double nextafter(double x, double y)
{
union {double f; uint64_t i;} ux={x}, uy={y};
- uint64_t ax, ay;
int e;
if (isnan(x) || isnan(y))
return x + y;
- if (ux.i == uy.i)
+ if (x == y)
return y;
- ax = ux.i & -1ULL/2;
- ay = uy.i & -1ULL/2;
- if (ax == 0) {
- if (ay == 0)
- return y;
+ if (x == 0.0)
ux.i = (uy.i & 1ULL<<63) | 1;
- } else if (ax > ay || ((ux.i ^ uy.i) & 1ULL<<63))
+ else if ((x < 0.0) == (x < y))
ux.i--;
else
ux.i++;
[-- Attachment #2: nextafter.patch --]
[-- Type: application/octet-stream, Size: 565 bytes --]
--- -/src/math/nextafter.c
+++ +/src/math/nextafter.c
@@ -3,20 +3,15 @@
double nextafter(double x, double y)
{
union {double f; uint64_t i;} ux={x}, uy={y};
- uint64_t ax, ay;
int e;
if (isnan(x) || isnan(y))
return x + y;
- if (ux.i == uy.i)
+ if (x == y)
return y;
- ax = ux.i & -1ULL/2;
- ay = uy.i & -1ULL/2;
- if (ax == 0) {
- if (ay == 0)
- return y;
+ if (x == 0.0)
ux.i = (uy.i & 1ULL<<63) | 1;
- } else if (ax > ay || ((ux.i ^ uy.i) & 1ULL<<63))
+ else if ((x < 0.0) == (x < y))
ux.i--;
else
ux.i++;
next reply other threads:[~2021-08-10 6:26 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-10 6:23 Stefan Kanthak [this message]
2021-08-10 21:34 ` Szabolcs Nagy
2021-08-10 22:53 ` Stefan Kanthak
2021-08-11 2:40 ` Rich Felker
2021-08-11 15:44 ` Stefan Kanthak
2021-08-11 16:09 ` Rich Felker
2021-08-11 16:50 ` Stefan Kanthak
2021-08-11 17:57 ` Rich Felker
2021-08-11 22:16 ` Szabolcs Nagy
2021-08-11 22:43 ` Stefan Kanthak
2021-08-12 0:59 ` Rich Felker
2021-08-11 8:23 ` Szabolcs Nagy
2021-08-13 12:04 ` [musl] [PATCH #2] " Stefan Kanthak
2021-08-13 15:59 ` Rich Felker
2021-08-13 18:30 ` Stefan Kanthak
2021-08-14 4:07 ` Damian McGuckin
2021-08-14 22:45 ` Szabolcs Nagy
2021-08-14 23:46 ` Szabolcs Nagy
2021-08-15 7:04 ` Stefan Kanthak
2021-08-15 7:46 ` Ariadne Conill
2021-08-15 13:59 ` Rich Felker
2021-08-15 14:57 ` Ariadne Conill
2021-08-15 8:24 ` Damian McGuckin
2021-08-15 14:03 ` Rich Felker
2021-08-15 15:10 ` Damian McGuckin
2021-08-15 14:56 ` Szabolcs Nagy
2021-08-15 15:19 ` Stefan Kanthak
2021-08-15 15:48 ` Rich Felker
2021-08-15 16:29 ` Stefan Kanthak
2021-08-15 16:49 ` Rich Felker
2021-08-15 20:52 ` Stefan Kanthak
2021-08-15 21:48 ` Rich Felker
2021-08-15 15:52 ` Ariadne Conill
2021-08-15 16:09 ` Rich Felker
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