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[PATCH] Speedup tanf range reduction
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>
- Cc: nd <nd at arm dot com>
- Date: Wed, 22 Aug 2018 12:29:12 +0000
- Subject: [PATCH] Speedup tanf range reduction
Speedup tanf range reduction by using the new sincosf range
reduction algorithm. Overall code quality is improved due to
inlining, so there is a speedup even if no range reduction is
required.
Passes GLIBC testsuite on AArch64. Some files are no longer
required - they are removed in the next patch.
tanf througput gains on Cortex-A72:
* |x| < M_PI_4 : 1.1x
* |x| < M_PI_2 : 1.2x
* |x| < 2 * M_PI: 1.5x
* |x| < 120.0 : 1.6x
* |x| < Inf : 12.1x
ChangeLog:
2018-08-22 Wilco Dijkstra <wdijkstr@arm.com>
* sysdeps/ieee754/flt-32/s_tanf.c (__tanf): Use fast range reduction.
--
diff --git a/sysdeps/ieee754/flt-32/s_tanf.c b/sysdeps/ieee754/flt-32/s_tanf.c
index ba3af54913669e4abdfd864307856ec44138f9b9..a397665c4bab7785049935ef526472afedf82e34 100644
--- a/sysdeps/ieee754/flt-32/s_tanf.c
+++ b/sysdeps/ieee754/flt-32/s_tanf.c
@@ -21,6 +21,30 @@ static char rcsid[] = "$NetBSD: s_tanf.c,v 1.4 1995/05/10 20:48:20 jtc Exp $";
#include <math.h>
#include <math_private.h>
#include <libm-alias-float.h>
+#include "s_sincosf.h"
+
+static inline int32_t
+rem_pio2f (float x, float *y)
+{
+ double dx = x;
+ int n;
+ const sincos_t *p = &__sincosf_table[0];
+
+ if (__glibc_likely (abstop12 (x) < abstop12 (120.0f)))
+ dx = reduce_fast (dx, p, &n);
+ else
+ {
+ uint32_t xi = asuint (x);
+ int sign = xi >> 31;
+
+ dx = reduce_large (xi, &n);
+ dx = sign ? -dx : dx;
+ }
+
+ y[0] = dx;
+ y[1] = dx - y[0];
+ return n;
+}
float __tanf(float x)
{
@@ -42,7 +66,7 @@ float __tanf(float x)
/* argument reduction needed */
else {
- n = __ieee754_rem_pio2f(x,y);
+ n = rem_pio2f(x,y);
return __kernel_tanf(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even
-1 -- n odd */
}