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/*
* Speed-optimized CRC32 using slicing-by-eight algorithm
* Instruction set: i386
* Optimized for: i686
*
* This code has been put into the public domain by its authors:
* Original code by Igor Pavlov <http://7-zip.org/>
* Position-independent version by Lasse Collin <lasse.collin@tukaani.org>
*
* This code needs lzma_crc32_table, which can be created using the
* following C code:
uint32_t lzma_crc32_table[8][256];
void
init_table(void)
{
// IEEE-802.3 (CRC32)
static const uint32_t poly32 = UINT32_C(0xEDB88320);
// Castagnoli (CRC32C)
// static const uint32_t poly32 = UINT32_C(0x82F63B78);
// Koopman
// static const uint32_t poly32 = UINT32_C(0xEB31D82E);
for (size_t s = 0; s < 8; ++s) {
for (size_t b = 0; b < 256; ++b) {
uint32_t r = s == 0 ? b : lzma_crc32_table[s - 1][b];
for (size_t i = 0; i < 8; ++i) {
if (r & 1)
r = (r >> 1) ^ poly32;
else
r >>= 1;
}
lzma_crc32_table[s][b] = r;
}
}
}
* The prototype of the CRC32 function:
* extern uint32_t lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc);
*/
.text
.globl lzma_crc32
.type lzma_crc32, @function
.align 16
lzma_crc32:
/*
* Register usage:
* %eax crc
* %esi buf
* %edi size or buf + size
* %ebx lzma_crc32_table
* %ebp Table index
* %ecx Temporary
* %edx Temporary
*/
pushl %ebx
pushl %esi
pushl %edi
pushl %ebp
movl 0x14(%esp), %esi /* buf */
movl 0x18(%esp), %edi /* size */
movl 0x1C(%esp), %eax /* crc */
/*
* Store the address of lzma_crc32_table to %ebx. This is needed to
* get position-independent code (PIC).
*/
call .L_PIC
.L_PIC:
popl %ebx
addl $_GLOBAL_OFFSET_TABLE_+[.-.L_PIC], %ebx
movl lzma_crc32_table@GOT(%ebx), %ebx
/* Complement the initial value. */
notl %eax
.align 16
.L_align:
/*
* Check if there is enough input to use slicing-by-eight.
* We need 16 bytes, because the loop pre-reads eight bytes.
*/
cmpl $16, %edi
jl .L_rest
/* Check if we have reached alignment of eight bytes. */
testl $7, %esi
jz .L_slice
/* Calculate CRC of the next input byte. */
movzbl (%esi), %ebp
incl %esi
movzbl %al, %ecx
xorl %ecx, %ebp
shrl $8, %eax
xorl (%ebx, %ebp, 4), %eax
decl %edi
jmp .L_align
.align 4
.L_slice:
/*
* If we get here, there's at least 16 bytes of aligned input
* available. Make %edi multiple of eight bytes. Store the possible
* remainder over the "size" variable in the argument stack.
*/
movl %edi, 0x18(%esp)
andl $-8, %edi
subl %edi, 0x18(%esp)
/*
* Let %edi be buf + size - 8 while running the main loop. This way
* we can compare for equality to determine when exit the loop.
*/
addl %esi, %edi
subl $8, %edi
/* Read in the first eight aligned bytes. */
xorl (%esi), %eax
movl 4(%esi), %ecx
movzbl %cl, %ebp
.L_loop:
movl 0x0C00(%ebx, %ebp, 4), %edx
movzbl %ch, %ebp
xorl 0x0800(%ebx, %ebp, 4), %edx
shrl $16, %ecx
xorl 8(%esi), %edx
movzbl %cl, %ebp
xorl 0x0400(%ebx, %ebp, 4), %edx
movzbl %ch, %ebp
xorl (%ebx, %ebp, 4), %edx
movzbl %al, %ebp
/*
* Read the next four bytes, for which the CRC is calculated
* on the next interation of the loop.
*/
movl 12(%esi), %ecx
xorl 0x1C00(%ebx, %ebp, 4), %edx
movzbl %ah, %ebp
shrl $16, %eax
xorl 0x1800(%ebx, %ebp, 4), %edx
movzbl %ah, %ebp
movzbl %al, %eax
movl 0x1400(%ebx, %eax, 4), %eax
addl $8, %esi
xorl %edx, %eax
xorl 0x1000(%ebx, %ebp, 4), %eax
/* Check for end of aligned input. */
cmpl %edi, %esi
movzbl %cl, %ebp
jne .L_loop
/*
* Process the remaining eight bytes, which we have already
* copied to %ecx and %edx.
*/
movl 0x0C00(%ebx, %ebp, 4), %edx
movzbl %ch, %ebp
xorl 0x0800(%ebx, %ebp, 4), %edx
shrl $16, %ecx
movzbl %cl, %ebp
xorl 0x0400(%ebx, %ebp, 4), %edx
movzbl %ch, %ebp
xorl (%ebx, %ebp, 4), %edx
movzbl %al, %ebp
xorl 0x1C00(%ebx, %ebp, 4), %edx
movzbl %ah, %ebp
shrl $16, %eax
xorl 0x1800(%ebx, %ebp, 4), %edx
movzbl %ah, %ebp
movzbl %al, %eax
movl 0x1400(%ebx, %eax, 4), %eax
addl $8, %esi
xorl %edx, %eax
xorl 0x1000(%ebx, %ebp, 4), %eax
/* Copy the number of remaining bytes to %edi. */
movl 0x18(%esp), %edi
.L_rest:
/* Check for end of input. */
testl %edi, %edi
jz .L_return
/* Calculate CRC of the next input byte. */
movzbl (%esi), %ebp
incl %esi
movzbl %al, %ecx
xorl %ecx, %ebp
shrl $8, %eax
xorl (%ebx, %ebp, 4), %eax
decl %edi
jmp .L_rest
.L_return:
/* Complement the final value. */
notl %eax
popl %ebp
popl %edi
popl %esi
popl %ebx
ret
.size lzma_crc32, .-lzma_crc32
/*
* This is needed to support non-executable stack. It's ugly to
* use __linux__ here, but I don't know a way to detect when
* we are using GNU assembler.
*/
#if defined(__ELF__) && defined(__linux__)
.section .note.GNU-stack,"",@progbits
#endif
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