/* * match.S -- optimized version of longest_match() * based on the similar work by Gilles Vollant, and Brian Raiter, written 1998 * * This is free software; you can redistribute it and/or modify it * under the terms of the BSD License. Use by owners of Che Guevarra * parafernalia is prohibited, where possible, and highly discouraged * elsewhere. */ #ifndef NO_UNDERLINE # define match_init _match_init # define longest_match _longest_match #endif #define scanend ebx #define scanendw bx #define chainlenwmask edx /* high word: current chain len low word: s->wmask */ #define curmatch rsi #define curmatchd esi #define windowbestlen r8 #define scanalign r9 #define scanalignd r9d #define window r10 #define bestlen r11 #define bestlend r11d #define scanstart r12d #define scanstartw r12w #define scan r13 #define nicematch r14d #define limit r15 #define limitd r15d #define prev rcx /* * The 258 is a "magic number, not a parameter -- changing it * breaks the hell loose */ #define MAX_MATCH (258) #define MIN_MATCH (3) #define MIN_LOOKAHEAD (MAX_MATCH + MIN_MATCH + 1) #define MAX_MATCH_8 ((MAX_MATCH + 7) & ~7) /* stack frame offsets */ #define LocalVarsSize (112) #define _chainlenwmask ( 8-LocalVarsSize)(%rsp) #define _windowbestlen (16-LocalVarsSize)(%rsp) #define save_r14 (24-LocalVarsSize)(%rsp) #define save_rsi (32-LocalVarsSize)(%rsp) #define save_rbx (40-LocalVarsSize)(%rsp) #define save_r12 (56-LocalVarsSize)(%rsp) #define save_r13 (64-LocalVarsSize)(%rsp) #define save_r15 (80-LocalVarsSize)(%rsp) /* * On AMD64 the first argument of a function (in our case -- the pointer to * deflate_state structure) is passed in %rdi, hence our offsets below are * all off of that. */ #ifndef STRUCT_OFFSET # define STRUCT_OFFSET (0) #endif #define dsWSize ( 56 + STRUCT_OFFSET)(%rdi) #define dsWMask ( 64 + STRUCT_OFFSET)(%rdi) #define dsWindow ( 72 + STRUCT_OFFSET)(%rdi) #define dsPrev ( 88 + STRUCT_OFFSET)(%rdi) #define dsMatchLen (136 + STRUCT_OFFSET)(%rdi) #define dsPrevMatch (140 + STRUCT_OFFSET)(%rdi) #define dsStrStart (148 + STRUCT_OFFSET)(%rdi) #define dsMatchStart (152 + STRUCT_OFFSET)(%rdi) #define dsLookahead (156 + STRUCT_OFFSET)(%rdi) #define dsPrevLen (160 + STRUCT_OFFSET)(%rdi) #define dsMaxChainLen (164 + STRUCT_OFFSET)(%rdi) #define dsGoodMatch (180 + STRUCT_OFFSET)(%rdi) #define dsNiceMatch (184 + STRUCT_OFFSET)(%rdi) .globl match_init, longest_match .text /* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */ longest_match: /* * Retrieve the function arguments. %curmatch will hold cur_match * throughout the entire function (passed via rsi on amd64). * rdi will hold the pointer to the deflate_state (first arg on amd64) */ mov %rsi, save_rsi mov %rbx, save_rbx mov %r12, save_r12 mov %r13, save_r13 mov %r14, save_r14 mov %r15, save_r15 /* uInt wmask = s->w_mask; */ /* unsigned chain_length = s->max_chain_length; */ /* if (s->prev_length >= s->good_match) { */ /* chain_length >>= 2; */ /* } */ movl dsPrevLen, %eax movl dsGoodMatch, %ebx cmpl %ebx, %eax movl dsWMask, %eax movl dsMaxChainLen, %chainlenwmask jl LastMatchGood shrl $2, %chainlenwmask LastMatchGood: /* chainlen is decremented once beforehand so that the function can */ /* use the sign flag instead of the zero flag for the exit test. */ /* It is then shifted into the high word, to make room for the wmask */ /* value, which it will always accompany. */ decl %chainlenwmask shll $16, %chainlenwmask orl %eax, %chainlenwmask /* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead; */ movl dsNiceMatch, %eax movl dsLookahead, %ebx cmpl %eax, %ebx jl LookaheadLess movl %eax, %ebx LookaheadLess: movl %ebx, %nicematch /* register Bytef *scan = s->window + s->strstart; */ mov dsWindow, %window movl dsStrStart, %limitd lea (%limit, %window), %scan /* Determine how many bytes the scan ptr is off from being */ /* dword-aligned. */ mov %scan, %scanalign negl %scanalignd andl $3, %scanalignd /* IPos limit = s->strstart > (IPos)MAX_DIST(s) ? */ /* s->strstart - (IPos)MAX_DIST(s) : NIL; */ movl dsWSize, %eax subl $MIN_LOOKAHEAD, %eax xorl %ecx, %ecx subl %eax, %limitd cmovng %ecx, %limitd /* int best_len = s->prev_length; */ movl dsPrevLen, %bestlend /* Store the sum of s->window + best_len in %windowbestlen locally, and in memory. */ lea (%window, %bestlen), %windowbestlen mov %windowbestlen, _windowbestlen /* register ush scan_start = *(ushf*)scan; */ /* register ush scan_end = *(ushf*)(scan+best_len-1); */ /* Posf *prev = s->prev; */ movzwl (%scan), %scanstart movzwl -1(%scan, %bestlen), %scanend mov dsPrev, %prev /* Jump into the main loop. */ movl %chainlenwmask, _chainlenwmask jmp LoopEntry .balign 16 /* do { * match = s->window + cur_match; * if (*(ushf*)(match+best_len-1) != scan_end || * *(ushf*)match != scan_start) continue; * [...] * } while ((cur_match = prev[cur_match & wmask]) > limit * && --chain_length != 0); * * Here is the inner loop of the function. The function will spend the * majority of its time in this loop, and majority of that time will * be spent in the first ten instructions. */ LookupLoop: andl %chainlenwmask, %curmatchd movzwl (%prev, %curmatch, 2), %curmatchd cmpl %limitd, %curmatchd jbe LeaveNow subl $0x00010000, %chainlenwmask js LeaveNow LoopEntry: cmpw -1(%windowbestlen, %curmatch), %scanendw jne LookupLoop cmpw %scanstartw, (%window, %curmatch) jne LookupLoop /* Store the current value of chainlen. */ movl %chainlenwmask, _chainlenwmask /* %scan is the string under scrutiny, and %prev to the string we */ /* are hoping to match it up with. In actuality, %esi and %edi are */ /* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is */ /* initialized to -(MAX_MATCH_8 - scanalign). */ mov $(-MAX_MATCH_8), %rdx lea (%curmatch, %window), %windowbestlen lea MAX_MATCH_8(%windowbestlen, %scanalign), %windowbestlen lea MAX_MATCH_8(%scan, %scanalign), %prev /* the prefetching below makes very little difference... */ prefetcht1 (%windowbestlen, %rdx) prefetcht1 (%prev, %rdx) /* * Test the strings for equality, 8 bytes at a time. At the end, * adjust %rdx so that it is offset to the exact byte that mismatched. * * It should be confessed that this loop usually does not represent * much of the total running time. Replacing it with a more * straightforward "rep cmpsb" would not drastically degrade * performance -- unrolling it, for example, makes no difference. */ #undef USE_SSE /* works, but is 6-7% slower, than non-SSE... */ LoopCmps: #ifdef USE_SSE /* Preload the SSE registers */ movdqu (%windowbestlen, %rdx), %xmm1 movdqu (%prev, %rdx), %xmm2 pcmpeqb %xmm2, %xmm1 movdqu 16(%windowbestlen, %rdx), %xmm3 movdqu 16(%prev, %rdx), %xmm4 pcmpeqb %xmm4, %xmm3 movdqu 32(%windowbestlen, %rdx), %xmm5 movdqu 32(%prev, %rdx), %xmm6 pcmpeqb %xmm6, %xmm5 movdqu 48(%windowbestlen, %rdx), %xmm7 movdqu 48(%prev, %rdx), %xmm8 pcmpeqb %xmm8, %xmm7 /* Check the comparisions' results */ pmovmskb %xmm1, %rax notw %ax bsfw %ax, %ax jnz LeaveLoopCmps add $16, %rdx pmovmskb %xmm3, %rax notw %ax bsfw %ax, %ax jnz LeaveLoopCmps add $16, %rdx pmovmskb %xmm5, %rax notw %ax bsfw %ax, %ax jnz LeaveLoopCmps add $16, %rdx pmovmskb %xmm7, %rax notw %ax bsfw %ax, %ax jnz LeaveLoopCmps add $16, %rdx jmp LoopCmps LeaveLoopCmps: add %rax, %rdx #else mov (%windowbestlen, %rdx), %rax xor (%prev, %rdx), %rax jnz LeaveLoopCmps add $8, %rdx jnz LoopCmps jmp LenMaximum # if 0 /* * This three-liner is tantalizingly simple, but bsf is a slow instruction, * and the complicated alternative down below is quite a bit faster. Sad... */ LeaveLoopCmps: bsf %rax, %rax /* find the first non-zero bit */ shrl $3, %eax /* divide by 8 to get the byte */ add %rax, %rdx # else LeaveLoopCmps: testl $0xFFFFFFFF, %eax /* Check the first 4 bytes */ jnz Check16 add $4, %rdx shr $32, %rax Check16: testw $0xFFFF, %ax jnz LenLower add $2, %rdx shrl $16, %eax LenLower: subb $1, %al adc $0, %rdx # endif #endif /* Calculate the length of the match. If it is longer than MAX_MATCH, */ /* then automatically accept it as the best possible match and leave. */ lea (%prev, %rdx), %rax sub %scan, %rax cmpl $MAX_MATCH, %eax jge LenMaximum /* If the length of the match is not longer than the best match we */ /* have so far, then forget it and return to the lookup loop. */ cmpl %bestlend, %eax jg LongerMatch mov _windowbestlen, %windowbestlen mov dsPrev, %prev movl _chainlenwmask, %edx jmp LookupLoop /* s->match_start = cur_match; */ /* best_len = len; */ /* if (len >= nice_match) break; */ /* scan_end = *(ushf*)(scan+best_len-1); */ LongerMatch: movl %eax, %bestlend movl %curmatchd, dsMatchStart cmpl %nicematch, %eax jge LeaveNow lea (%window, %bestlen), %windowbestlen mov %windowbestlen, _windowbestlen movzwl -1(%scan, %rax), %scanend mov dsPrev, %prev movl _chainlenwmask, %chainlenwmask jmp LookupLoop /* Accept the current string, with the maximum possible length. */ LenMaximum: movl $MAX_MATCH, %bestlend movl %curmatchd, dsMatchStart /* if ((uInt)best_len <= s->lookahead) return (uInt)best_len; */ /* return s->lookahead; */ LeaveNow: movl dsLookahead, %eax cmpl %eax, %bestlend cmovngl %bestlend, %eax LookaheadRet: /* Restore the registers and return from whence we came. */ mov save_rsi, %rsi mov save_rbx, %rbx mov save_r12, %r12 mov save_r13, %r13 mov save_r14, %r14 mov save_r15, %r15 ret match_init: ret