AMD Typewriter x86 사용자 설명서

Replace Branches with Computation in 3DNow!™ Code

22007E/0—November 1999

AMD Athlon™ Processor x86 Code Optimization

Example 4:

C code:

#define PI 3.14159265358979323
float x,z,r,res;
/* 0 <= r <= PI/4 */
z = abs(x)
if (z < 1) {
res = r;
}
else {
res = PI/2-r;
}

3DNow! code:

;in:

MM0 = x

;

MM1 = r

;out: MM1 = res
MOVQ

MM5, mabs ; mask to clear sign bit

MOVQ

MM6, one ; 1.0

PAND

MM0, MM5 ; z=abs(x)

PCMPGTD MM6, MM0 ; z < 1 ? 0xffffffff : 0
MOVQ

MM4, pio2 ; pi/2

PFSUB

MM4, MM1 ; pi/2-r

PANDN

MM6, MM4 ; z < 1 ? 0 : pi/2-r

PFMAX

MM1, MM6 ; res = z < 1 ? r : pi/2-r