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| author | bde <bde@FreeBSD.org> | 2005-11-28 06:15:10 +0000 |
|---|---|---|
| committer | bde <bde@FreeBSD.org> | 2005-11-28 06:15:10 +0000 |
| commit | 1f04771fa4ce46cff003cc3d9f0d04d58130d491 (patch) | |
| tree | f2e67e23f4cd2c4e86127d82410aeba707c49dac /lib | |
| parent | 9553dd02c7b046157e6d70b512ac45f21c97299a (diff) | |
| download | FreeBSD-src-1f04771fa4ce46cff003cc3d9f0d04d58130d491.zip FreeBSD-src-1f04771fa4ce46cff003cc3d9f0d04d58130d491.tar.gz | |
Exploit skew-symmetry to avoid an operation: -sin(x-A) = sin(A-x). This
gives a tiny but hopefully always free optimization in the 2 quadrants
to which it applies. On Athlons, it reduces maximum latency by 4 cycles
in these quadrants but has usually has a smaller effect on total time
(typically ~2 cycles (~5%), but sometimes 8 cycles when the compiler
generates poor code).
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/msun/src/s_cosf.c | 4 | ||||
| -rw-r--r-- | lib/msun/src/s_sinf.c | 4 |
2 files changed, 4 insertions, 4 deletions
diff --git a/lib/msun/src/s_cosf.c b/lib/msun/src/s_cosf.c index 42664e2..84fbc6d 100644 --- a/lib/msun/src/s_cosf.c +++ b/lib/msun/src/s_cosf.c @@ -48,7 +48,7 @@ cosf(float x) } if(ix<=0x407b53d1) { /* |x| ~<= 5*pi/4 */ if(ix<=0x4016cbe3) /* |x| ~<= 3pi/4 */ - return -__kernel_sindf(x - c1pio2); + return __kernel_sindf(c1pio2 - x); else return -__kernel_cosdf(x - c2pio2); } @@ -67,7 +67,7 @@ cosf(float x) n = __ieee754_rem_pio2f(x,y); switch(n&3) { case 0: return __kernel_cosdf((double)y[0]+y[1]); - case 1: return -__kernel_sindf((double)y[0]+y[1]); + case 1: return __kernel_sindf(-(double)y[0]-y[1]); case 2: return -__kernel_cosdf((double)y[0]+y[1]); default: return __kernel_sindf((double)y[0]+y[1]); diff --git a/lib/msun/src/s_sinf.c b/lib/msun/src/s_sinf.c index dc46a68..5842014 100644 --- a/lib/msun/src/s_sinf.c +++ b/lib/msun/src/s_sinf.c @@ -53,7 +53,7 @@ sinf(float x) else return -__kernel_cosdf(x + s1pio2); } else - return -__kernel_sindf(x + (hx > 0 ? -s2pio2 : s2pio2)); + return __kernel_sindf((hx > 0 ? s2pio2 : -s2pio2) - x); } if(ix<=0x40e231d5) { /* |x| ~<= 9*pi/4 */ if(ix<=0x40afeddf) { /* |x| ~<= 7*pi/4 */ @@ -74,7 +74,7 @@ sinf(float x) switch(n&3) { case 0: return __kernel_sindf((double)y[0]+y[1]); case 1: return __kernel_cosdf((double)y[0]+y[1]); - case 2: return -__kernel_sindf((double)y[0]+y[1]); + case 2: return __kernel_sindf(-(double)y[0]-y[1]); default: return -__kernel_cosdf((double)y[0]+y[1]); } |
