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Optimizing for SIMD Integer Applications 4
4-25
Absolute Value
Use Example 4-18 to compute |x|, where x is signed. This example
assumes signed words to be the operands.
movq MM2, MM0 ; make a copy of source1 (A)
pcmpgtw MM0, MM1 ; create mask of
; source1>source2 (A>B)
movq MM4, MM2 ; make another copy of A
pxor MM2, MM1 ; create the intermediate value of
; the swap operation - xor(A,B)
pand MM2, MM0 ; create a mask of 0s and xor(A,B)
; elements. Where A>B there will
; be a value xor(A,B) and where
; A<=B there will be 0.
pxor MM4, MM2 ; minima-xor(A, swap mask)
pxor MM1, MM2 ; maxima-xor(B, swap mask)
psubw MM1, MM4 ; absolute difference =
; maxima-minima
Example 4-18 Computing Absolute Value
; Input:
; MM0 signed source operand
; Output:
; MM1 ABS(MMO)
pxor MM1, MM1 ; set MM1 to all zeros
psubw MM1, MM0 ; make each MM1 word contain the
; negative of each MM0 word
pmaxsw MM1, MM0 ; MM1 will contain only the positive
; (larger) values - the absolute value
Example 4-17 Absolute Difference of Signed Numbers (continued)