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# SIMD SSE2 dot product
# Equivalent to the following C code:
# long dotprod(signed short *a,signed short *b,int cnt)
# {
# long sum = 0;
# cnt *= 8;
# while(cnt--)
# sum += *a++ + *b++;
# return sum;
# }
# a and b must be 128-bit aligned
# Copyright 2001, Phil Karn KA9Q
# May be used under the terms of the GNU Lesser General Public License (LGPL)
.global dotprod_sse2_assist
.type dotprod_sse2_assist,@function
pushl %ebp
movl %esp,%ebp
pushl %esi
pushl %edi
pushl %ecx
pushl %ebx
movl 8(%ebp),%esi # a
movl 12(%ebp),%edi # b
movl 16(%ebp),%ecx # cnt
pxor %xmm0,%xmm0 # clear running sum (in two 32-bit halves)
# SSE2 dot product loop unrolled 4 times, crunching 32 terms per loop
.align 16
.Loop1: subl $4,%ecx
jl .Loop1Done
movdqa (%esi),%xmm1
pmaddwd (%edi),%xmm1
paddd %xmm1,%xmm0
movdqa 16(%esi),%xmm1
pmaddwd 16(%edi),%xmm1
paddd %xmm1,%xmm0
movdqa 32(%esi),%xmm1
pmaddwd 32(%edi),%xmm1
paddd %xmm1,%xmm0
movdqa 48(%esi),%xmm1
addl $64,%esi
pmaddwd 48(%edi),%xmm1
addl $64,%edi
paddd %xmm1,%xmm0
jmp .Loop1
addl $4,%ecx
# SSE2 dot product loop, not unrolled, crunching 4 terms per loop
# This could be redone as Duff's Device on the unrolled loop above
.Loop2: subl $1,%ecx
jl .Loop2Done
movdqa (%esi),%xmm1
addl $16,%esi
pmaddwd (%edi),%xmm1
addl $16,%edi
paddd %xmm1,%xmm0
jmp .Loop2
movdqa %xmm0,%xmm1
psrldq $8,%xmm0
paddd %xmm1,%xmm0
movd %xmm0,%eax # right-hand word to eax
psrldq $4,%xmm0
movd %xmm0,%ebx
addl %ebx,%eax
popl %ebx
popl %ecx
popl %edi
popl %esi
movl %ebp,%esp
popl %ebp