/* * Copyright (c) 2000-2013 Apple Inc. All rights reserved. * * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. The rights granted to you under the License * may not be used to create, or enable the creation or redistribution of, * unlawful or unlicensed copies of an Apple operating system, or to * circumvent, violate, or enable the circumvention or violation of, any * terms of an Apple operating system software license agreement. * * Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ */ /* This file contains x86_64 hand optimized implementation of WKdm memory page compressor. int WKdm_compress (WK_word* src_buf, WK_word* dest_buf, WK_word* scratch, unsigned int bytes_budget); input : src_buf : address of input page (length = 1024 words) dest_buf : address of output buffer (may not be 16-byte aligned) scratch : a 16-byte aligned 4k bytes scratch memory provided by the caller, bytes_budget : a given byte target in compression output : if the input buffer can be compressed within the given byte budget, the dest_buf is written with compressed data and the function returns with number of bytes for the compressed data o.w., the function returns -1 to signal that the input data can not be compressed with the given byte budget. During the scan and tag process, each word that can not be compressed will be written to dest_buf, followed by a 12-bytes header + 256-bytes tag area. When the functions returns -1, dest_buf is filled with all those words that can not be compressed and should be considered undefined. The worst-case scenario is that all words can not be compressed. Hence, the minimum size requirement for dest_buf should be 12+256+4096 = 4364 bytes to prevent from memory fault. The 4th argument bytes_budget is the target compress budget in bytes. Should the input page can be compressed within the budget, the compressed data is written to *dest_buf, and the function returns the number of compressed bytes. Otherwise, the function returns -1 (to signal to the caller that the page can not be compressed). WKdm Compression algorithm is briefly stated as follows: There is a dynamically updated dictionary consisting of 16 words. Each dictionary word is initialized to 1 at the point of entry to the function. For a nonzero input word x, its 8-bits (10-bits scaled up) is used to determine a corresponding word from the dictionary, represented by dict_index (4-bits) and dict_word (32-bits). a. k = (x>>10)&255; // 8-bit hash table index b. dict_index = hashTable[k]; // 4-bit dictionary index, hashTable[] is fixed c. dict_word = dictionary[dict_index]; // 32-bit dictionary word, dictionary[] is dynamically updated Each input word x is classified/tagged into 4 classes : 0 : x = 0 1 : (x>>10) == (dict_word>>10), bits 10:31 of the input word match a dictionary word 2 : (x>>10) != (dict_word>>10), the above condition (22 higher bits matched) is not met, meaning a dictionary miss 3 : (x == dict_word), the exact input word is in the dictionary For each class, different numbers of bits are needed for the decompressor to reproduce the original input word. 0 : 2-bits tag (32->2 compression) 1 : 2-bits tag + 4-bits dict_index + 10-bits lower bits (32->16 compression) 2 : 2-bits tag + 32-bits new word (32->34 expansion) 3 : 2-bits tag + 4-bits dict_index (32->6 compression) It is obvious now that WKdm compress algorithm works well for pages where there are lots of zero words (32->2) and/or there are freqeunt repeats of some word patterns (32->6). the output bit stream (*dest_buf) consists of a. 12 bytes header b. 256 bytes for 1024 packed tags c. (varying number of) words for new words not matched to dictionary word. d. (varying number of) 32-bit words for packed 4-bit dict_indices (for class 1 and 3) e. (varying number of) 32-bit words for packed 10-bit low bits (for class 1) the header is actually of 3 words that specify the ending offset (in 32-bit words) from the start of the bit stream of c,d,e, respectively. Note that there might be padding bits in d (if the number of dict_indices does not divide by 8), and there are 2/12/22 padding bits for packing 3/2/1 low 10-bits in a 32-bit word. The WKdm compress algorithm 1st runs a scan and classification pass, tagging and write unpacked data into temporary buffers. It follows by packing those data into the output buffer. The temp buffers are uint8_t tempTagsArray[1024]; // temporary saving for tags before final packing uint8_t tempQPosArray[1024]; // temporary saving for dict_indices before final packing uint16_t tempLowBitsArray[1024]; // temporary saving for partially matched lower 10 bits before final packing Since the new words (that can not matched fully or partially to the dictionary) are stored right after the header and the tags section and need no packing, we directly write them to the destination buffer. uint32_t *new_word = dest_buf+3+64; // 3 words for header, 64 words for tags, new words come right after the tags. Now since we are given a byte budget for this compressor, we can monitor the byte usage on the fly in the scanning and tagging pass. bytes_budget -= 12 + 256; // header and tags (1024 * 2 /8 = 256 bytes) whenever an input word is classified as class 2 : bytes_budget-=4; if (bytes_budget<=0) exit -1; when writing the 8 4-bits/3 10-bits, monitor bytes_budget and exit -1 when byte_budget <=0; without showing the bit budget management, the pseudo code is given as follows: uint8_t *tags=tempTagsArray; uint8_t *dict=tempQPosArray; uint8_t *partial=tempLowBitsArray; for (i=0;i<1024;i++) { x = *src_buf++; if (x == 0) { // zero, 2-bits tag *tags++ = 0; } else { // find dict_index and dict_word from x k = (x>>10)&255; dict_index = hashTable[k]; dict_word = dictionary[dict_index]; if (dict_word == x) { // exactly match // 2-bits tag + 4-bits table index *tags++ = 3; *dict++ = dict_index; } else if (((x^dict_word)>>10)==0) { // 22 higher bits matched // 2-bits tag + 4-bits table index + 10-bits lower partial *tags++ = 1; *dict++ = dict_index; *partial++ = x &0x3ff; dictionary[dict_index] = x; } else { // not matched // 2-bits tag + 32-bits new word *tags++ = 2; *new_word++ = x; dictionary[dict_index] = x; } } } after this classification/tagging pass is completed, the 3 temp buffers are packed into the output *dest_buf: 1. 1024 tags are packed into 256 bytes right after the 12-bytes header 2. dictionary indices (4-bits each) are packed into are right after the new words section 3. 3 low 10-bits are packed into a 32-bit word, this is after the dictionary indices section. cclee, 11/30/12 */ .text .align 4,0x90 .globl _WKdm_compress_new _WKdm_compress_new: pushq %rbp movq %rsp, %rbp pushq %r15 pushq %r14 pushq %r13 pushq %r12 pushq %rbx subq $(24+64), %rsp #define tempTagsArray 64(%rsp) #define tempLowBitsArray 72(%rsp) #define next_tag %r8 #define next_input_word %rdi #define end_of_input %r13 #define next_full_patt %rbx #define dict_location %rcx #define next_qp %r10 #define dictionary %rsp #define scratch %r11 #define dest_buf %r12 #define hashTable %r14 #define tempQPosArray %r15 #define next_low_bits %rsi #define byte_count %r9d movq %rsi, %r12 // dest_buf movq %rdx, scratch // scratch = dictionary movq %rdx, tempTagsArray // &tempTagsArray[0] movq %rdx, next_tag // next_tag always points to the one following the current tag leaq 1024(%rdx), tempQPosArray // &tempQPosArray[0] movq tempQPosArray, next_qp // next_qp leaq 4096(%rdi), end_of_input // end_of_input = src_buf + num_input_words leaq 268(%rsi), %rbx // dest_buf + [TAGS_AREA_OFFSET + (num_input_words / 16)]*4 movl %ecx, byte_count subl $(12+256), byte_count // header + tags jle L_budgetExhausted // PRELOAD_DICTIONARY; movl $1, 0(dictionary) movl $1, 4(dictionary) movl $1, 8(dictionary) movl $1, 12(dictionary) movl $1, 16(dictionary) movl $1, 20(dictionary) movl $1, 24(dictionary) movl $1, 28(dictionary) movl $1, 32(dictionary) movl $1, 36(dictionary) movl $1, 40(dictionary) movl $1, 44(dictionary) movl $1, 48(dictionary) movl $1, 52(dictionary) movl $1, 56(dictionary) movl $1, 60(dictionary) leaq 2048(%rdx), %rax // &tempLowBitsArray[0] movq %rax, tempLowBitsArray // save for later reference movq %rax, next_low_bits // next_low_bits leaq _hashLookupTable_new(%rip), hashTable // hash look up table jmp L_scan_loop .align 4,0x90 L_RECORD_ZERO: movb $0, -1(next_tag) // *next_tag = ZERO; addq $4, next_input_word // next_input_word++; cmpq next_input_word, end_of_input // end_of_input vs next_input_word jbe L_done_search L_scan_loop: movl (next_input_word), %edx incq next_tag // next_tag++ testl %edx, %edx je L_RECORD_ZERO // if (input_word==0) RECORD_ZERO movl %edx, %eax // a copy of input_word shrl $10, %eax // input_high_bits = HIGH_BITS(input_word); movzbl %al, %eax // 8-bit index to the Hash Table movsbq (hashTable,%rax),%rax // HASH_TO_DICT_BYTE_OFFSET(input_word) leaq (dictionary, %rax), dict_location // ((char*) dictionary) + HASH_TO_DICT_BYTE_OFFSET(input_word)); movl (dict_location), %eax // dict_word = *dict_location; addq $4, next_input_word // next_input_word++ cmpl %eax, %edx // dict_word vs input_word je L_RECORD_EXACT // if identical, RECORD_EXACT xorl %edx, %eax shrl $10, %eax // HIGH_BITS(dict_word) je L_RECORD_PARTIAL // if identical, RECORD_PARTIAL L_RECORD_MISS: movl %edx, (next_full_patt) // *next_full_patt = input_word; addq $4, next_full_patt // next_full_patt++ movl %edx, (dict_location) // *dict_location = input_word movb $2, -1(next_tag) // *next_tag = 2 for miss subl $4, byte_count // fill in a new 4-bytes word jle L_budgetExhausted cmpq next_input_word, end_of_input // end_of_input vs next_input_word ja L_scan_loop L_done_search: // SET_QPOS_AREA_START(dest_buf,next_full_patt); movq next_full_patt, %rax // next_full_patt subq dest_buf, %rax // next_full_patt - dest_buf sarq $2, %rax // offset in 4-bytes movl %eax, %r13d // r13d = (next_full_patt - dest_buf) movl %eax, 0(dest_buf) // dest_buf[0] = next_full_patt - dest_buf decq next_tag cmpq next_tag, tempTagsArray // &tempTagsArray[0] vs next_tag jae L13 // if (&tempTagsArray[0] >= next_tag), skip the following // boundary_tmp = WK_pack_2bits(tempTagsArray, (WK_word *) next_tag, dest_buf + HEADER_SIZE_IN_WORDS); movq dest_buf, %rdi // dest_buf movq tempTagsArray, %rcx // &tempTagsArray[0] .align 4,0x90 L_pack_2bits: movq 8(%rcx), %rax // w3 addq $16, %rcx // tempTagsArray += 16; shlq $4, %rax addq $4, %rdi // dest_buf += 4; orq -16(%rcx), %rax // w3 movq %rax, %rdx shrq $30, %rax orl %edx, %eax cmpq %rcx, next_tag // cmp next_tag vs dest_buf movl %eax, 8(%rdi) // save at *(dest_buf + HEADER_SIZE_IN_WORDS) ja L_pack_2bits // if (next_tag > dest_buf) repeat L_pack_2bits /* Pack the queue positions into the area just after the full words. */ L13: mov next_qp, %rax // next_qp sub tempQPosArray, %rax // num_bytes_to_pack = next_qp - (char *) tempQPosArray; addl $7, %eax // num_bytes_to_pack+7 shrl $3, %eax // num_packed_words = (num_bytes_to_pack + 7) >> 3 shll $2, %eax // turn into bytes subl %eax, byte_count // jl L_budgetExhausted shrl $1, %eax // num_source_words = num_packed_words * 2; leaq (tempQPosArray,%rax,4), %rcx // endQPosArray = tempQPosArray + num_source_words cmpq %rcx, next_qp // next_qp vs endQPosArray jae L16 // if (next_qp >= endQPosArray) skip the following zero paddings movq %rcx, %rax subq next_qp, %rax subl $4, %eax jl 1f .align 4,0x90 0: movl $0, (next_qp) addq $4, next_qp subl $4, %eax jge 0b 1: testl $2, %eax je 1f movw $0, (next_qp) addq $2, next_qp 1: testl $1, %eax je 1f movb $0, (next_qp) addq $1, next_qp 1: L16: movq next_full_patt, %rdi // next_full_patt cmpq tempQPosArray, %rcx // endQPosArray vs tempQPosArray jbe L20 // if (endQPosArray <= tempQPosArray) skip the following movq tempQPosArray, %rdx // tempQPosArray /* byte_count -= (rcx - tempQPosArray)/2 */ .align 4,0x90 L_pack_4bits: movl 4(%rdx), %eax // src_next[1] addq $8, %rdx // src_next += 2; sall $4, %eax // (src_next[1] << 4) addq $4, %rdi // dest_next++; orl -8(%rdx), %eax // temp = src_next[0] | (src_next[1] << 4) cmpq %rdx, %rcx // source_end vs src_next movl %eax, -4(%rdi) // dest_next[0] = temp; ja L_pack_4bits // while (src_next < source_end) repeat the loop // SET_LOW_BITS_AREA_START(dest_buf,boundary_tmp); movq %rdi, %rax // boundary_tmp subq dest_buf, %rax // boundary_tmp - dest_buf movq %rax, %r13 // boundary_tmp - dest_buf shrq $2, %r13 // boundary_tmp - dest_buf in words L20: movl %r13d, 4(dest_buf) // dest_buf[1] = boundary_tmp - dest_buf movq tempLowBitsArray, %rcx // tempLowBitsArray movq next_low_bits, %rbx // next_low_bits subq %rcx, %rbx // next_low_bits - tempLowBitsArray (in bytes) sarq $1, %rbx // num_tenbits_to_pack (in half-words) #define size %ebx subl $3, size // pre-decrement num_tenbits_to_pack by 3 jl 1f // if num_tenbits_to_pack < 3, skip the following loop .align 4,0x90 0: movzwl 4(%rcx), %eax // w2 addq $6, %rcx // next w0/w1/w2 triplet sall $10, %eax // w1 << 10 or -4(%rcx), %ax // w1 addq $4, %rdi // dest_buf++ sall $10, %eax // w1 << 10 or -6(%rcx), %ax // (w0) | (w1<<10) | (w2<<20) subl $4, byte_count // fill in a new 4-bytes word jle L_budgetExhausted subl $3, size // num_tenbits_to_pack-=3 movl %eax, -4(%rdi) // pack w0,w1,w2 into 1 dest_buf word jge 0b // if no less than 3 elements, back to loop head 1: addl $3, size // post-increment num_tenbits_to_pack by 3 je 3f // if num_tenbits_to_pack is a multiple of 3, skip the following movzwl (%rcx), %eax // w0 subl $1, size // num_tenbits_to_pack-- je 2f // movzwl 2(%rcx), %edx // w1 sall $10, %edx // w1 << 10 orl %edx, %eax // w0 | (w1<<10) 2: subl $4, byte_count // fill in a new 4-bytes word jle L_budgetExhausted movl %eax, (%rdi) // write the final dest_buf word addq $4, %rdi // dest_buf++ 3: movq %rdi, %rax // boundary_tmp subq dest_buf, %rax // boundary_tmp - dest_buf shrq $2, %rax // boundary_tmp - dest_buf in terms of words movl %eax, 8(dest_buf) // SET_LOW_BITS_AREA_END(dest_buf,boundary_tmp) shlq $2, %rax // boundary_tmp - dest_buf in terms of bytes L_done: // restore registers and return addq $(24+64), %rsp popq %rbx popq %r12 popq %r13 popq %r14 popq %r15 leave ret .align 4 L_budgetExhausted: mov $-1, %rax jmp L_done .align 4,0x90 L_RECORD_EXACT: subq dictionary, %rcx // dict_location - dictionary sarq $2, %rcx // divide by 4 for word offset movb $3, -1(next_tag) // *next_tag = 3 for exact movb %cl, (next_qp) // *next_qp = word offset (4-bit) incq next_qp // next_qp++ cmpq next_input_word, end_of_input // end_of_input vs next_input_word ja L_scan_loop jmp L_done_search .align 4,0x90 L_RECORD_PARTIAL: movq %rcx, %rax // dict_location movb $1, -1(next_tag) // *next_tag = 1 for partial matched subq dictionary, %rax // dict_location - dictionary movl %edx, (%rcx) // *dict_location = input_word; sarq $2, %rax // offset in 32-bit word movb %al, (next_qp) // update *next_qp andl $1023, %edx // lower 10 bits incq next_qp // next_qp++ mov %dx, (next_low_bits) // save next_low_bits addq $2, next_low_bits // next_low_bits++ cmpq next_input_word, end_of_input // end_of_input vs next_input_word ja L_scan_loop jmp L_done_search