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Use fabs[f]() instead of bit fiddling for setting absolute values.

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This makes little difference in float precision, but in double
precision gives a speedup of about 30% on amd64 (A64 CPU) and i386
(A64).  This depends on fabs[f]() being inline and efficient.  The
bit fiddling (or any use of SET_HIGH_WORD(), which libm does too
much because it was best on old 32-bit machines) always causes
packing overheads and sometimes causes stalls in the packing, since
it operates on only part of a variable in the double precision case.
It apparently did cause stalls in a critical path here.
This commit is contained in:
Bruce Evans 2008-03-30 18:07:12 +00:00
parent c0c7ddd3a8
commit 42ee187c3c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=177751
2 changed files with 4 additions and 4 deletions
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4
lib/msun/src/e_hypot.c
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@ -60,8 +60,8 @@ __ieee754_hypot(double x, double y)
GET_HIGH_WORD(hb,y);
hb &= 0x7fffffff;
if(hb > ha) {a=y;b=x;j=ha; ha=hb;hb=j;} else {a=x;b=y;}
SET_HIGH_WORD(a,ha); /* a <- |a| */
SET_HIGH_WORD(b,hb); /* b <- |b| */
a = fabs(a);
b = fabs(b);
if((ha-hb)>0x3c00000) {return a+b;} /* x/y > 2**60 */
k=0;
if(ha > 0x5f300000) { /* a>2**500 */

4
lib/msun/src/e_hypotf.c
View File

@ -30,8 +30,8 @@ __ieee754_hypotf(float x, float y)
GET_FLOAT_WORD(hb,y);
hb &= 0x7fffffff;
if(hb > ha) {a=y;b=x;j=ha; ha=hb;hb=j;} else {a=x;b=y;}
SET_FLOAT_WORD(a,ha); /* a <- |a| */
SET_FLOAT_WORD(b,hb); /* b <- |b| */
a = fabsf(a);
b = fabsf(b);
if((ha-hb)>0xf000000) {return a+b;} /* x/y > 2**30 */
k=0;
if(ha > 0x58800000) { /* a>2**50 */