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1/* Intel SIMD SSE2 implementation of Viterbi ACS butterflies
2   for 256-state (k=9) convolutional code
3   Copyright 2004 Phil Karn, KA9Q
4   This code may be used under the terms of the GNU Lesser General Public License (LGPL)
5
6   void update_viterbi29_blk_sse2(struct v29 *vp,unsigned char *syms,int nbits) ;
7*/
8
9	# SSE2 (128-bit integer SIMD) version
10	# Requires Pentium 4 or better
11	# These are offsets into struct v29, defined in viterbi29.h
12	.set DP,512
13	.set OLDMETRICS,516
14	.set NEWMETRICS,520
15
16	.text
17	.global update_viterbi29_blk_sse2,Branchtab29_sse2
18	.type update_viterbi29_blk_sse2,@function
19	.align 16
20
21update_viterbi29_blk_sse2:
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
340:	movl OLDMETRICS(%edx),%esi	# esi -> old metrics
35	movl NEWMETRICS(%edx),%edi	# edi -> new metrics
36	movl DP(%edx),%edx	# edx -> decisions
37
381:	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,%xmm6		# xmm6[0] = first symbol
47	movb 1(%ebx),%al
48	movd %eax,%xmm5		# xmm5[0] = second symbol
49	addl $2,%ebx
50	movl %ebx,12(%ebp)
51
52	punpcklbw %xmm6,%xmm6	# xmm6[1] = xmm6[0]
53	punpcklbw %xmm5,%xmm5
54	movdqa thirtyones,%xmm7
55	pshuflw $0,%xmm6,%xmm6	# copy low word to low 3
56	pshuflw $0,%xmm5,%xmm5
57	punpcklqdq %xmm6,%xmm6  # propagate to all 16
58	punpcklqdq %xmm5,%xmm5
59	# xmm6 now contains first symbol in each byte, xmm5 the second
60
61	movdqa thirtyones,%xmm7
62
63	# each invocation of this macro does 16 butterflies in parallel
64	.MACRO butterfly GROUP
65	# compute branch metrics
66	movdqa Branchtab29_sse2+(16*\GROUP),%xmm4
67	movdqa Branchtab29_sse2+128+(16*\GROUP),%xmm3
68	pxor %xmm6,%xmm4
69	pxor %xmm5,%xmm3
70	pavgb %xmm3,%xmm4
71	psrlw $3,%xmm4
72
73	pand %xmm7,%xmm4	# xmm4 contains branch metrics
74
75	movdqa (16*\GROUP)(%esi),%xmm0	# Incoming path metric, high bit = 0
76	movdqa ((16*\GROUP)+128)(%esi),%xmm3	# Incoming path metric, high bit = 1
77	movdqa %xmm0,%xmm2
78	movdqa %xmm3,%xmm1
79	paddusb %xmm4,%xmm0
80	paddusb %xmm4,%xmm3
81
82	# invert branch metrics
83	pxor %xmm7,%xmm4
84
85	paddusb %xmm4,%xmm1
86	paddusb %xmm4,%xmm2
87
88	# Find survivors, leave in mm0,2
89	pminub %xmm1,%xmm0
90	pminub %xmm3,%xmm2
91	# get decisions, leave in mm1,3
92	pcmpeqb %xmm0,%xmm1
93	pcmpeqb %xmm2,%xmm3
94
95	# interleave and store new branch metrics in mm0,2
96	movdqa %xmm0,%xmm4
97	punpckhbw %xmm2,%xmm0	# interleave second 16 new metrics
98	punpcklbw %xmm2,%xmm4	# interleave first 16 new metrics
99	movdqa %xmm0,(32*\GROUP+16)(%edi)
100	movdqa %xmm4,(32*\GROUP)(%edi)
101
102	# interleave decisions & store
103	movdqa %xmm1,%xmm4
104	punpckhbw %xmm3,%xmm1
105	punpcklbw %xmm3,%xmm4
106	# work around bug in gas due to Intel doc error
107	.byte 0x66,0x0f,0xd7,0xd9	# pmovmskb %xmm1,%ebx
108	shll $16,%ebx
109	.byte 0x66,0x0f,0xd7,0xc4	# pmovmskb %xmm4,%eax
110	orl %eax,%ebx
111	movl %ebx,(4*\GROUP)(%edx)
112	.endm
113
114	# invoke macro 8 times for a total of 128 butterflies
115	butterfly GROUP=0
116	butterfly GROUP=1
117	butterfly GROUP=2
118	butterfly GROUP=3
119	butterfly GROUP=4
120	butterfly GROUP=5
121	butterfly GROUP=6
122	butterfly GROUP=7
123
124	addl $32,%edx		# bump decision pointer
125
126	# see if we have to normalize
127	movl (%edi),%eax	# extract first output metric
128	andl $255,%eax
129	cmp $50,%eax		# is it greater than 50?
130	movl $0,%eax
131	jle done		# No, no need to normalize
132
133	# Normalize by finding smallest metric and subtracting it
134	# from all metrics
135	movdqa (%edi),%xmm0
136	pminub 16(%edi),%xmm0
137	pminub 32(%edi),%xmm0
138	pminub 48(%edi),%xmm0
139	pminub 64(%edi),%xmm0
140	pminub 80(%edi),%xmm0
141	pminub 96(%edi),%xmm0
142	pminub 112(%edi),%xmm0
143	pminub 128(%edi),%xmm0
144	pminub 144(%edi),%xmm0
145	pminub 160(%edi),%xmm0
146	pminub 176(%edi),%xmm0
147	pminub 192(%edi),%xmm0
148	pminub 208(%edi),%xmm0
149	pminub 224(%edi),%xmm0
150	pminub 240(%edi),%xmm0
151
152	# crunch down to single lowest metric
153	movdqa %xmm0,%xmm1
154	psrldq $8,%xmm0     # the count to psrldq is bytes, not bits!
155	pminub %xmm1,%xmm0
156	movdqa %xmm0,%xmm1
157	psrlq $32,%xmm0
158	pminub %xmm1,%xmm0
159	movdqa %xmm0,%xmm1
160	psrlq $16,%xmm0
161	pminub %xmm1,%xmm0
162	movdqa %xmm0,%xmm1
163	psrlq $8,%xmm0
164	pminub %xmm1,%xmm0
165
166	punpcklbw %xmm0,%xmm0	# lowest 2 bytes
167	pshuflw $0,%xmm0,%xmm0  # lowest 8 bytes
168	punpcklqdq %xmm0,%xmm0	# all 16 bytes
169
170	# xmm0 now contains lowest metric in all 16 bytes
171	# subtract it from every output metric
172	movdqa (%edi),%xmm1
173	psubusb %xmm0,%xmm1
174	movdqa %xmm1,(%edi)
175	movdqa 16(%edi),%xmm1
176	psubusb %xmm0,%xmm1
177	movdqa %xmm1,16(%edi)
178	movdqa 32(%edi),%xmm1
179	psubusb %xmm0,%xmm1
180	movdqa %xmm1,32(%edi)
181	movdqa 48(%edi),%xmm1
182	psubusb %xmm0,%xmm1
183	movdqa %xmm1,48(%edi)
184	movdqa 64(%edi),%xmm1
185	psubusb %xmm0,%xmm1
186	movdqa %xmm1,64(%edi)
187	movdqa 80(%edi),%xmm1
188	psubusb %xmm0,%xmm1
189	movdqa %xmm1,80(%edi)
190	movdqa 96(%edi),%xmm1
191	psubusb %xmm0,%xmm1
192	movdqa %xmm1,96(%edi)
193	movdqa 112(%edi),%xmm1
194	psubusb %xmm0,%xmm1
195	movdqa %xmm1,112(%edi)
196	movdqa 128(%edi),%xmm1
197	psubusb %xmm0,%xmm1
198	movdqa %xmm1,128(%edi)
199	movdqa 144(%edi),%xmm1
200	psubusb %xmm0,%xmm1
201	movdqa %xmm1,144(%edi)
202	movdqa 160(%edi),%xmm1
203	psubusb %xmm0,%xmm1
204	movdqa %xmm1,160(%edi)
205	movdqa 176(%edi),%xmm1
206	psubusb %xmm0,%xmm1
207	movdqa %xmm1,176(%edi)
208	movdqa 192(%edi),%xmm1
209	psubusb %xmm0,%xmm1
210	movdqa %xmm1,192(%edi)
211	movdqa 208(%edi),%xmm1
212	psubusb %xmm0,%xmm1
213	movdqa %xmm1,208(%edi)
214	movdqa 224(%edi),%xmm1
215	psubusb %xmm0,%xmm1
216	movdqa %xmm1,224(%edi)
217	movdqa 240(%edi),%xmm1
218	psubusb %xmm0,%xmm1
219	movdqa %xmm1,240(%edi)
220
221done:
222	# swap metrics
223	movl %esi,%eax
224	movl %edi,%esi
225	movl %eax,%edi
226	jmp 1b
227
2282:	movl 8(%ebp),%ebx	# ebx = vp
229	# stash metric pointers
230	movl %esi,OLDMETRICS(%ebx)
231	movl %edi,NEWMETRICS(%ebx)
232	movl %edx,DP(%ebx)	# stash incremented value of vp->dp
233	xorl %eax,%eax
234err:	popl %ebx
235	popl %edx
236	popl %edi
237	popl %esi
238	popl %ebp
239	ret
240
241	.data
242	.align 16
243thirtyones:
244	.byte 31,31,31,31,31,31,31,31,31,31,31,31,31,31,31,31
245
246