Annotation of OpenXM_contrib/gmp/mpn/x86/pentium/diveby3.asm, Revision 1.1.1.2
1.1 maekawa 1: dnl Intel P5 mpn_divexact_by3 -- mpn division by 3, expecting no remainder.
2:
1.1.1.2 ! ohara 3: dnl Copyright 2000, 2002 Free Software Foundation, Inc.
1.1 maekawa 4: dnl
5: dnl This file is part of the GNU MP Library.
6: dnl
7: dnl The GNU MP Library is free software; you can redistribute it and/or
8: dnl modify it under the terms of the GNU Lesser General Public License as
9: dnl published by the Free Software Foundation; either version 2.1 of the
10: dnl License, or (at your option) any later version.
11: dnl
12: dnl The GNU MP Library is distributed in the hope that it will be useful,
13: dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
14: dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15: dnl Lesser General Public License for more details.
16: dnl
17: dnl You should have received a copy of the GNU Lesser General Public
18: dnl License along with the GNU MP Library; see the file COPYING.LIB. If
19: dnl not, write to the Free Software Foundation, Inc., 59 Temple Place -
20: dnl Suite 330, Boston, MA 02111-1307, USA.
21:
22: include(`../config.m4')
23:
24:
1.1.1.2 ! ohara 25: C P5: 15.0 cycles/limb
! 26:
! 27:
1.1 maekawa 28: C mp_limb_t mpn_divexact_by3c (mp_ptr dst, mp_srcptr src, mp_size_t size,
29: C mp_limb_t carry);
30:
31: defframe(PARAM_CARRY,16)
32: defframe(PARAM_SIZE, 12)
33: defframe(PARAM_SRC, 8)
34: defframe(PARAM_DST, 4)
35:
36: dnl multiplicative inverse of 3, modulo 2^32
37: deflit(INVERSE_3, 0xAAAAAAAB)
38:
39: dnl ceil(b/3), ceil(b*2/3) and floor(b*2/3) where b=2^32
40: deflit(ONE_THIRD_CEIL, 0x55555556)
41: deflit(TWO_THIRDS_CEIL, 0xAAAAAAAB)
42: deflit(TWO_THIRDS_FLOOR, 0xAAAAAAAA)
43:
1.1.1.2 ! ohara 44: TEXT
1.1 maekawa 45: ALIGN(8)
46:
47: PROLOGUE(mpn_divexact_by3c)
48: deflit(`FRAME',0)
49:
50: movl PARAM_SRC, %ecx
51: movl PARAM_SIZE, %edx
52:
53: decl %edx
54: jnz L(two_or_more)
55:
56: movl (%ecx), %edx
57: movl PARAM_CARRY, %eax C risk of cache bank clash here
58:
59: movl PARAM_DST, %ecx
60: subl %eax, %edx
61:
62: sbbl %eax, %eax C 0 or -1
63:
64: imull $INVERSE_3, %edx, %edx
65:
66: negl %eax C 0 or 1
67: cmpl $ONE_THIRD_CEIL, %edx
68:
69: sbbl $-1, %eax C +1 if edx>=ceil(b/3)
70: cmpl $TWO_THIRDS_CEIL, %edx
71:
72: sbbl $-1, %eax C +1 if edx>=ceil(b*2/3)
73: movl %edx, (%ecx)
74:
75: ret
76:
77:
78: L(two_or_more):
79: C eax
80: C ebx
81: C ecx src
82: C edx size-1
83: C esi
84: C edi
85: C ebp
86:
87: pushl %ebx FRAME_pushl()
88: pushl %esi FRAME_pushl()
89:
90: pushl %edi FRAME_pushl()
91: pushl %ebp FRAME_pushl()
92:
93: movl PARAM_DST, %edi
94: movl PARAM_CARRY, %esi
95:
96: movl (%ecx), %eax C src low limb
97: xorl %ebx, %ebx
98:
99: sub %esi, %eax
100: movl $TWO_THIRDS_FLOOR, %esi
101:
102: leal (%ecx,%edx,4), %ecx C &src[size-1]
103: leal (%edi,%edx,4), %edi C &dst[size-1]
104:
105: adcl $0, %ebx C carry, 0 or 1
106: negl %edx C -(size-1)
107:
108:
109: C The loop needs a source limb ready at the top, which leads to one limb
110: C handled separately at the end, and the special case above for size==1.
111: C There doesn't seem to be any scheduling that would keep the speed but move
112: C the source load and carry subtract up to the top.
113: C
114: C The destination cache line prefetching adds 1 cycle to the loop but is
115: C considered worthwhile. The slowdown is a factor of 1.07, but will prevent
116: C repeated write-throughs if the destination isn't in L1. A version using
117: C an outer loop to prefetch only every 8 limbs (a cache line) proved to be
118: C no faster, due to unavoidable branch mispreditions in the inner loop.
119: C
120: C setc is 2 cycles on P54, so an adcl is used instead. If the movl $0,%ebx
121: C could be avoided then the src limb fetch could pair up and save a cycle.
122: C This would probably mean going to a two limb loop with the carry limb
123: C alternately positive or negative, since an sbbl %ebx,%ebx will leave a
124: C value which is in the opposite sense to the preceding sbbl/adcl %ebx,%eax.
125: C
126: C A register is used for TWO_THIRDS_FLOOR because a cmp can't be done as
127: C "cmpl %edx, $n" with the immediate as the second operand.
128: C
129: C The "4" source displacement is in the loop rather than the setup because
130: C this gets L(top) aligned to 8 bytes at no cost.
131:
132: ALIGN(8)
133: L(top):
134: C eax source limb, carry subtracted
135: C ebx carry (0 or 1)
136: C ecx &src[size-1]
137: C edx counter, limbs, negative
138: C esi TWO_THIRDS_FLOOR
139: C edi &dst[size-1]
140: C ebp scratch (result limb)
141:
142: imull $INVERSE_3, %eax, %ebp
143:
144: cmpl $ONE_THIRD_CEIL, %ebp
145: movl (%edi,%edx,4), %eax C dst cache line prefetch
146:
147: sbbl $-1, %ebx C +1 if ebp>=ceil(b/3)
148: cmpl %ebp, %esi
149:
150: movl 4(%ecx,%edx,4), %eax C next src limb
151:
152: sbbl %ebx, %eax C and further -1 if ebp>=ceil(b*2/3)
153: movl $0, %ebx
154:
155: adcl $0, %ebx C new carry
156: movl %ebp, (%edi,%edx,4)
157:
158: incl %edx
159: jnz L(top)
160:
161:
162:
163: imull $INVERSE_3, %eax, %edx
164:
165: cmpl $ONE_THIRD_CEIL, %edx
166: movl %edx, (%edi)
167:
168: sbbl $-1, %ebx C +1 if edx>=ceil(b/3)
169: cmpl $TWO_THIRDS_CEIL, %edx
170:
171: sbbl $-1, %ebx C +1 if edx>=ceil(b*2/3)
172: popl %ebp
173:
174: movl %ebx, %eax
175: popl %edi
176:
177: popl %esi
178: popl %ebx
179:
180: ret
181:
182: EPILOGUE()
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to diveby3.asm CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [local] / OpenXM_contrib / gmp / mpn / x86 / pentium