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Speedup tanf range reduction

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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.

tanf throughput 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

	* sysdeps/ieee754/flt-32/s_tanf.c (__tanf): Use fast range reduction.
This commit is contained in:
Wilco Dijkstra 2018-08-23 12:38:16 +01:00
parent 561b0bec44
commit 900fb446eb
2 changed files with 32 additions and 1 deletions
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4
ChangeLog
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@ -1,3 +1,7 @@
2018-08-23 Wilco Dijkstra <wdijkstr@arm.com>
* sysdeps/ieee754/flt-32/s_tanf.c (__tanf): Use fast range reduction.
2018-08-22 DJ Delorie <dj@redhat.com>
* Makefile (testroot.pristine): New rules to initialize the

29
sysdeps/ieee754/flt-32/s_tanf.c
View file

@ -21,6 +21,33 @@ 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"
/* Reduce range of X to a multiple of PI/2. The modulo result is between
-PI/4 and PI/4 and returned as a high part y[0] and a low part y[1].
The low bit in the return value indicates the first or 2nd half of tanf. */
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 +69,7 @@ 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 */
}