Intel® 64 and IA-32 Architectures Optimization Reference Manual

OPTIMIZING FOR SIMD INTEGER APPLICATIONSExample 5-25. Big-Endian to Little-Endian Conversion Using PSHUFB__declspec(align(16)) BYTE bswapMASK[16] ={3,2,1,0, 7,6,5,4, 11,10,9,8, 15,14,13,12};lea eax, srclea ecx, dstmov edx, elCountmovaps xmm7, bswapMASKstart:movdqa xmm0, [eax]pshufb xmm0, xmm7movdqa [ecx], xmm0add eax, 16add ecx, 16sub edx, 4jnz start5.6.6 Clipping to an Arbitrary Range [High, Low]This section explains how to clip a values to a range [HIGH, LOW]. Specifically, if thevalue is less than LOW or greater than HIGH, then clip to LOW or HIGH, respectively.This technique uses the packed-add and packed-subtract instructions with saturation(signed or unsigned), which means that this technique can only be used on packedbyteand packed-word data types.The examples in this section use the constants PACKED_MAX and PACKED_MIN andshow operations on word values. For simplicity, we use the following constants(corresponding constants are used in case the operation is done on byte values):PACKED_MAX equals 0X7FFF7FFF7FFF7FFFPACKED_MIN equals 0X8000800080008000PACKED_LOW contains the value LOW in all four words of the packed-words data typePACKED_HIGH contains the value HIGH in all four words of the packed-words data typePACKED_USMAX all values equal 1HIGH_US adds the HIGH value to all data elements (4 words) of PACKED_MINLOW_US adds the LOW value to all data elements (4 words) of PACKED_MIN5.6.6.1 Highly Efficient ClippingFor clipping signed words to an arbitrary range, the PMAXSW and PMINSW instructionsmay be used. For clipping unsigned bytes to an arbitrary range, the PMAXUBand PMINUB instructions may be used.5-25