1 /* Intel SIMD (SSE) implementation of Viterbi ACS butterflies 2 for 64-state (k=7) convolutional code 3 Copyright 2001 Phil Karn, KA9Q 4 This code may be used under the terms of the GNU Lesser General Public License (LGPL) 5 6 int update_viterbi27_blk_sse(struct v27 *vp,unsigned char syms[],int nbits) ; 7 */ 8 9 # SSE (64-bit integer SIMD) version 10 # Requires Pentium III or better 11 12 # These are offsets into struct v27, defined in viterbi27.h 13 .set DP,128 14 .set OLDMETRICS,132 15 .set NEWMETRICS,136 16 .text 17 .global update_viterbi27_blk_sse,Branchtab27_sse 18 .type update_viterbi27_blk_sse,@function 19 .align 16 20 21 update_viterbi27_blk_sse: 22 pushl %ebp 23 movl %esp,%ebp 24 pushl %esi 25 pushl %edi 26 pushl %edx 27 pushl %ebx 28 29 movl 8(%ebp),%edx # edx = vp 30 testl %edx,%edx 31 jnz 0f 32 movl -1,%eax 33 jmp err 34 0: movl OLDMETRICS(%edx),%esi # esi -> old metrics 35 movl NEWMETRICS(%edx),%edi # edi -> new metrics 36 movl DP(%edx),%edx # edx -> decisions 37 38 1: movl 16(%ebp),%eax # eax = nbits 39 decl %eax 40 jl 2f # passed zero, we're done 41 movl %eax,16(%ebp) 42 43 xorl %eax,%eax 44 movl 12(%ebp),%ebx # %ebx = syms 45 movb (%ebx),%al 46 movd %eax,%mm6 # mm6[0] = first symbol 47 movb 1(%ebx),%al 48 movd %eax,%mm5 # mm5[0] = second symbol 49 addl $2,%ebx 50 movl %ebx,12(%ebp) 51 52 punpcklbw %mm6,%mm6 # mm6[1] = mm6[0] 53 punpcklbw %mm5,%mm5 54 movq thirtyones,%mm7 55 56 pshufw $0,%mm6,%mm6 # copy low word to upper 3 57 pshufw $0,%mm5,%mm5 58 # mm6 now contains first symbol in each byte, mm5 the second 59 60 # each invocation of this macro does 8 butterflies in parallel 61 .MACRO butterfly GROUP 62 # compute branch metrics 63 movq Branchtab27_sse+(8*\GROUP),%mm4 64 movq Branchtab27_sse+32+(8*\GROUP),%mm3 65 pxor %mm6,%mm4 66 pxor %mm5,%mm3 67 pavgb %mm3,%mm4 # mm4 contains branch metrics 68 psrlw $3,%mm4 69 pand %mm7,%mm4 70 71 movq (8*\GROUP)(%esi),%mm0 # Incoming path metric, high bit = 0 72 movq ((8*\GROUP)+32)(%esi),%mm3 # Incoming path metric, high bit = 1 73 movq %mm0,%mm2 74 movq %mm3,%mm1 75 paddusb %mm4,%mm0 76 paddusb %mm4,%mm3 77 78 # invert branch metrics. This works only because they're 5 bits 79 pxor %mm7,%mm4 80 81 paddusb %mm4,%mm1 82 paddusb %mm4,%mm2 83 84 # Find survivors, leave in mm0,2 85 pminub %mm1,%mm0 86 pminub %mm3,%mm2 87 # get decisions, leave in mm1,3 88 pcmpeqb %mm0,%mm1 89 pcmpeqb %mm2,%mm3 90 91 # interleave and store new branch metrics in mm0,2 92 movq %mm0,%mm4 93 punpckhbw %mm2,%mm0 # interleave second 8 new metrics 94 punpcklbw %mm2,%mm4 # interleave first 8 new metrics 95 movq %mm0,(16*\GROUP+8)(%edi) 96 movq %mm4,(16*\GROUP)(%edi) 97 98 # interleave decisions, accumulate into %ebx 99 movq %mm1,%mm4 100 punpckhbw %mm3,%mm1 101 punpcklbw %mm3,%mm4 102 # Due to an error in the Intel instruction set ref (the register 103 # fields are swapped), gas assembles pmovmskb incorrectly 104 # See http://mail.gnu.org/pipermail/bug-gnu-utils/2000-August/002341.html 105 .byte 0x0f,0xd7,0xc1 # pmovmskb %mm1,%eax 106 shll $((16*\GROUP+8)&31),%eax 107 orl %eax,%ebx 108 .byte 0x0f,0xd7,0xc4 # pmovmskb %mm4,%eax 109 shll $((16*\GROUP)&31),%eax 110 orl %eax,%ebx 111 .endm 112 113 # invoke macro 4 times for a total of 32 butterflies 114 xorl %ebx,%ebx # clear decisions 115 butterfly GROUP=0 116 butterfly GROUP=1 117 movl %ebx,(%edx) # stash first 32 decisions 118 xorl %ebx,%ebx 119 butterfly GROUP=2 120 butterfly GROUP=3 121 movl %ebx,4(%edx) # stash second 32 decisions 122 123 addl $8,%edx # bump decision pointer 124 125 # see if we have to normalize 126 movl (%edi),%eax # extract first output metric 127 andl $255,%eax 128 cmpl $150,%eax # is it greater than 150? 129 movl $0,%eax 130 jle done # No, no need to normalize 131 132 # Normalize by finding smallest metric and subtracting it 133 # from all metrics 134 movq (%edi),%mm0 135 pminub 8(%edi),%mm0 136 pminub 16(%edi),%mm0 137 pminub 24(%edi),%mm0 138 pminub 32(%edi),%mm0 139 pminub 40(%edi),%mm0 140 pminub 48(%edi),%mm0 141 pminub 56(%edi),%mm0 142 # mm0 contains 8 smallest metrics 143 # crunch down to single lowest metric 144 movq %mm0,%mm1 145 psrlq $32,%mm0 146 pminub %mm1,%mm0 147 movq %mm0,%mm1 148 psrlq $16,%mm0 149 pminub %mm1,%mm0 150 movq %mm0,%mm1 151 psrlq $8,%mm0 152 pminub %mm1,%mm0 153 punpcklbw %mm0,%mm0 # expand to all 8 bytes 154 pshufw $0,%mm0,%mm0 155 156 # mm0 now contains lowest metric in all 8 bytes 157 # subtract it from every output metric 158 # Trashes %mm7 159 .macro PSUBUSBM REG,MEM 160 movq \MEM,%mm7 161 psubusb \REG,%mm7 162 movq %mm7,\MEM 163 .endm 164 165 PSUBUSBM %mm0,(%edi) 166 PSUBUSBM %mm0,8(%edi) 167 PSUBUSBM %mm0,16(%edi) 168 PSUBUSBM %mm0,24(%edi) 169 PSUBUSBM %mm0,32(%edi) 170 PSUBUSBM %mm0,40(%edi) 171 PSUBUSBM %mm0,48(%edi) 172 PSUBUSBM %mm0,56(%edi) 173 174 movd %mm0,%eax 175 and $0xff,%eax 176 177 done: # swap metrics 178 movl %esi,%eax 179 movl %edi,%esi 180 movl %eax,%edi 181 jmp 1b 182 183 2: emms 184 movl 8(%ebp),%ebx # ebx = vp 185 # stash metric pointers 186 movl %esi,OLDMETRICS(%ebx) 187 movl %edi,NEWMETRICS(%ebx) 188 movl %edx,DP(%ebx) # stash incremented value of vp->dp 189 xorl %eax,%eax 190 err: popl %ebx 191 popl %edx 192 popl %edi 193 popl %esi 194 popl %ebp 195 196 ret 197 198 .data 199 200 .align 16 201 thirtyones: 202 .byte 31,31,31,31,31,31,31,31 203 204 205 206
