From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Subject: [PATCH] math: move i386 sqrt to C
Date: Tue, 7 Jan 2020 16:06:05 +0300 [thread overview]
Message-ID: <20200107130605.7618-1-amonakov@ispras.ru> (raw)
In-Reply-To: <alpine.LNX.2.20.13.2001051915090.31907@monopod.intra.ispras.ru>
[-- Attachment #1: Type: text/plain, Size: 733 bytes --]
---
Since union ldshape does not have a dedicated field for 32 least significant
bits of the x87 long double mantissa, keeping the original approach with
ux.i.m -= (fpsr & 0x200) - 0x100;
would lead to a 64-bit subtraction that is not trivial for the compiler to
optimize to 32-bit subtraction as done in the original assembly. Therefore
I have elected to change the approach and use
ux.i.m ^= (fpsr & 0x200) + 0x200;
which is easier to optimize to a 32-bit rather than 64-bit xor.
Thoughts?
src/math/i386/sqrt.c | 15 +++++++++++++++
src/math/i386/sqrt.s | 21 ---------------------
2 files changed, 15 insertions(+), 21 deletions(-)
create mode 100644 src/math/i386/sqrt.c
delete mode 100644 src/math/i386/sqrt.s
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0005-math-move-i386-sqrt-to-C.patch --]
[-- Type: text/x-patch; name="0005-math-move-i386-sqrt-to-C.patch", Size: 1103 bytes --]
diff --git a/src/math/i386/sqrt.c b/src/math/i386/sqrt.c
new file mode 100644
index 00000000..619df056
--- /dev/null
+++ b/src/math/i386/sqrt.c
@@ -0,0 +1,15 @@
+#include "libm.h"
+
+double sqrt(double x)
+{
+ union ldshape ux;
+ unsigned fpsr;
+ __asm__ ("fsqrt; fnstsw %%ax": "=t"(ux.f), "=a"(fpsr) : "0"(x));
+ if ((ux.i.m & 0x7ff) != 0x400)
+ return (double)ux.f;
+ /* Rounding to double would have encountered an exact halfway case.
+ Adjust mantissa downwards if fsqrt rounded up, else upwards.
+ (result of fsqrt could not have been exact) */
+ ux.i.m ^= (fpsr & 0x200) + 0x200;
+ return (double)ux.f;
+}
diff --git a/src/math/i386/sqrt.s b/src/math/i386/sqrt.s
deleted file mode 100644
index 57837e25..00000000
--- a/src/math/i386/sqrt.s
+++ /dev/null
@@ -1,21 +0,0 @@
-.global sqrt
-.type sqrt,@function
-sqrt: fldl 4(%esp)
- fsqrt
- fnstsw %ax
- sub $12,%esp
- fld %st(0)
- fstpt (%esp)
- mov (%esp),%ecx
- and $0x7ff,%ecx
- cmp $0x400,%ecx
- jnz 1f
- and $0x200,%eax
- sub $0x100,%eax
- sub %eax,(%esp)
- fstp %st(0)
- fldt (%esp)
-1: add $12,%esp
- fstpl 4(%esp)
- fldl 4(%esp)
- ret
next prev parent reply other threads:[~2020-01-07 13:06 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-05 16:35 math patches for moving bare asm to C inline asm Alexander Monakov
2020-01-05 16:36 ` [PATCH] math: move x86_64 fabs, fabsf to C with " Alexander Monakov
2020-01-05 20:05 ` Rich Felker
2020-01-05 21:32 ` Alexander Monakov
2020-01-05 22:43 ` Rich Felker
2020-01-06 8:17 ` Alexander Monakov
2020-01-06 8:40 ` [PATCH] math: move more x86-family fabs functions to C Alexander Monakov
2020-03-21 17:06 ` [musl] " Rich Felker
2020-01-06 16:50 ` [PATCH] math: move trivial x86-family sqrt " Alexander Monakov
2020-01-06 17:43 ` [PATCH] math: move i386 sqrtf " Alexander Monakov
2020-01-06 18:32 ` Pascal Cuoq
2020-01-09 15:55 ` Alexander Monakov
2020-01-09 17:00 ` Rich Felker
2020-01-09 21:00 ` Szabolcs Nagy
2020-01-09 22:00 ` Rich Felker
2020-01-09 23:18 ` Szabolcs Nagy
2020-01-10 2:07 ` Rich Felker
2020-01-10 9:17 ` Szabolcs Nagy
2020-01-14 17:59 ` [musl] " Alexander Monakov
2020-01-14 18:47 ` Szabolcs Nagy
2020-01-07 13:06 ` Alexander Monakov [this message]
2020-01-08 7:26 ` [PATCH] math: move i386 sqrt " Rich Felker
2020-03-21 17:53 ` [musl] " Rich Felker
2020-03-21 17:57 ` Rich Felker
2020-03-21 20:30 ` Alexander Monakov
2020-01-11 15:06 ` [PATCH] math: move x86_64 (l)lrint(f) functions " Alexander Monakov
2020-01-11 15:23 ` [PATCH] math: move more x86-family lrint " Alexander Monakov
2020-01-11 16:07 ` Rich Felker
2020-01-11 16:22 ` Rich Felker
2020-01-14 11:54 ` [musl] [PATCH] math: move x86-family rint " Alexander Monakov
2020-01-14 18:17 ` [musl] Q: dealing with missing removal of excess precision Alexander Monakov
2020-01-14 18:50 ` Szabolcs Nagy
2020-01-14 18:58 ` Rich Felker
2020-01-14 19:53 ` Alexander Monakov
2020-02-06 14:51 ` Rich Felker
2020-02-06 17:15 ` Alexander Monakov
2020-02-06 17:46 ` Rich Felker
2020-02-06 19:03 ` Rich Felker
2020-02-06 20:02 ` Rich Felker
2020-02-06 22:08 ` Szabolcs Nagy
2020-02-22 19:59 ` Rich Felker
2020-02-22 20:21 ` Alexander Monakov
2020-02-23 0:19 ` Rich Felker
2020-02-23 16:14 ` Alexander Monakov
2020-03-20 18:12 ` Rich Felker
2020-03-22 1:19 ` Rich Felker
2020-03-22 17:40 ` Alexander Monakov
2020-03-22 17:53 ` Rich Felker
2020-03-22 18:51 ` Alexander Monakov
2020-03-22 19:10 ` Rich Felker
2020-03-22 19:46 ` Alexander Monakov
2020-01-14 20:41 ` [musl] [PATCH] math: move x86-family remainder functions to C Alexander Monakov
2020-01-15 6:54 ` Szabolcs Nagy
2020-01-15 15:44 ` [musl] [PATCH] math: move x86-family fmod " Alexander Monakov
2020-01-16 21:00 ` [musl] [PATCH] math: add x86_64 remquol Alexander Monakov
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