ULONG *pulSrcMipmap, ULONG *pulDstMipmap, PIX pixWidth, PIX pixHeight;

    __asm {
      pxor    mm0,mm0
      mov     ebx,D [pixWidth]
      mov     esi,D [pulSrcMipmap]
      mov     edi,D [pulDstMipmap]
      mov     edx,D [pixHeight]
rowLoop:
      mov     ecx,D [pixWidth]
pixLoopN:           
      movd    mm1,D [esi+ 0]        // up-left
      movd    mm2,D [esi+ 4]        // up-right
      movd    mm3,D [esi+ ebx*8 +0] // down-left
      movd    mm4,D [esi+ ebx*8 +4] // down-right
      punpcklbw mm1,mm0
      punpcklbw mm2,mm0
      punpcklbw mm3,mm0
      punpcklbw mm4,mm0
      paddw   mm1,mm2
      paddw   mm1,mm3
      paddw   mm1,mm4
      paddw   mm1,Q [mmRounder]
      psrlw   mm1,2
      packuswb mm1,mm0
      movd    D [edi],mm1
      // advance to next pixel
      add     esi,4*2
      add     edi,4
      dec     ecx
      jnz     pixLoopN
      // advance to next row
      lea     esi,[esi+ ebx*8] // skip one row in source mip-map
      dec     edx
      jnz     rowLoop
      emms
    }