From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Subject: [musl] [PATCH] math: add x86_64 remquol
Date: Fri, 17 Jan 2020 00:00:51 +0300 [thread overview]
Message-ID: <20200116210051.19494-1-amonakov@ispras.ru> (raw)
In-Reply-To: <alpine.LNX.2.20.13.2001051915090.31907@monopod.intra.ispras.ru>
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---
So proud of this one <3
(this is not a rewrite as x86_64 remquol.s does not exist, but that
looks unintentional and i386 remquo versions need similar rewrites anyway)
src/math/x86_64/remquol.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
create mode 100644 src/math/x86_64/remquol.c
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diff --git a/src/math/x86_64/remquol.c b/src/math/x86_64/remquol.c
new file mode 100644
index 00000000..60eef089
--- /dev/null
+++ b/src/math/x86_64/remquol.c
@@ -0,0 +1,32 @@
+#include <math.h>
+
+long double remquol(long double x, long double y, int *quo)
+{
+ signed char *cx = (void *)&x, *cy = (void *)&y;
+ /* By ensuring that addresses of x and y cannot be discarded,
+ * this empty asm guides GCC into representing extraction of
+ * their sign bits as memory loads rather than making x and y
+ * not-address-taken internally and using bitfield operations,
+ * which in the end wouldn't work out, as extraction from FPU
+ * registers needs to go through memory anyway. This way GCC
+ * should manage to use incoming stack slots without spills. */
+ __asm__ ("" :: "X"(cx), "X"(cy));
+
+ long double t = x;
+ unsigned fpsr;
+ do __asm__ ("fprem1; fnstsw %%ax" : "+t"(t), "=a"(fpsr) : "u"(y));
+ while (fpsr & 0x400);
+ /* C0, C1, C3 flags in x87 status word carry low bits of quotient:
+ * 15 14 13 12 11 10 9 8
+ * . C3 . . . C2 C1 C0
+ * . b1 . . . 0 b0 b2 */
+ unsigned char i = fpsr >> 8;
+ i = i>>4 | i<<4;
+ /* i[5:2] is now {b0 b2 ? b1}. Retrieve {0 b2 b1 b0} via
+ * in-register table lookup. */
+ unsigned qbits = 0x7575313164642020 >> (i & 60);
+ qbits &= 7;
+
+ *quo = (cx[9]^cy[9]) < 0 ? -qbits : qbits;
+ return t;
+}
prev parent reply other threads:[~2020-01-16 21:01 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 ` [PATCH] math: move i386 sqrt " Alexander Monakov
2020-01-08 7:26 ` 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 ` Alexander Monakov [this message]
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