AMD 250 manual Example 5 C Code, Example 5 3DNow! Code, 140

Software Optimization Guide for AMD64 Processors 25112 Rev. 3.06 September 2005

Example 5: C Code

#define PI 3.14159265358979323 float x, y ,xa ,ya ,r ,res; int xs, df;

xs = x < 0 ? 1 : 0; xa = fabs(x);

ya = fabs(y); df = (xa < ya); if (xs && df) {

res = PI / 2 + r;

}else if (xs) { res = PI - r;

}else if (df) { res = PI/2 - r;

}else {

res = r;

}

Example 5: 3DNow!™ Code

;In: MM0 = r

;MM1 = y

;MM2 = x

;Out: MM0 = res

movq	mm7, sgn	; Mask	to	extract sign bit
movq	mm6, sgn	; Mask	to	extract sign bit
movq	mm5, mabs	; Mask	to	clear sign bit
pand	mm7, mm2	; xs =	sign(x)
pand	mm1, mm5	; ya =	abs(y)
pand	mm2, mm5	; xa = abs(x)
movq	mm6, mm1	; y
pcmpgtd	mm6, mm2	; df = (xa < ya) ? 0xffffffff : 0
pslld	mm6, 31	; df = bit 31
movq	mm5, mm7	; xs
pxor	mm7, mm6	; xs ^ df		? 0x80000000 : 0
movq	mm3, npio2	; -pi / 2
pxor	mm5, mm3	; xs ? pi		/ 2 : -pi / 2
psrad	mm6, 31	; df ? 0xffffffff : 0
pandn	mm6, mm5	; xs ? (df ? 0 : pi / 2) : (df ? 0 : -pi / 2)
pfsub	mm6, mm3	; pr = pi		/ 2 + (xs ? (df ? 0 : pi / 2) :
		; (df ? 0 : -pi / 2))
por	mm0, mm7	; ar = xs		^ df ? -r : r
pfadd	mm0, mm6	; res = ar + pr

140 Branch Optimizations Chapter 6