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/*
* Speed-optimized CRC64 using slicing-by-four algorithm
* Instruction set: i386
* Optimized for: i686
*
* This code has been put into the public domain by its authors:
* Igor Pavlov <http://7-zip.org/>
* Lasse Collin <lasse.collin@tukaani.org>
*
* This code needs lzma_crc64_table, which can be created using the
* following C code:
uint64_t lzma_crc64_table[4][256];
void
init_table(void)
{
static const uint64_t poly64 = UINT64_C(0xC96C5795D7870F42);
for (size_t s = 0; s < 4; ++s) {
for (size_t b = 0; b < 256; ++b) {
uint64_t r = s == 0 ? b : lzma_crc64_table[s - 1][b];
for (size_t i = 0; i < 8; ++i) {
if (r & 1)
r = (r >> 1) ^ poly64;
else
r >>= 1;
}
lzma_crc64_table[s][b] = r;
}
}
}
* The prototype of the CRC64 function:
* extern uint64_t lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc);
*/
.text
.globl lzma_crc64
.type lzma_crc64, @function
.align 16
lzma_crc64:
/*
* Register usage:
* %eax crc LSB
* %edx crc MSB
* %esi buf
* %edi size or buf + size
* %ebx lzma_crc64_table
* %ebp Table index
* %ecx Temporary
*/
pushl %ebx
pushl %esi
pushl %edi
pushl %ebp
movl 0x14(%esp), %esi /* buf */
movl 0x18(%esp), %edi /* size */
movl 0x1C(%esp), %eax /* crc LSB */
movl 0x20(%esp), %edx /* crc MSB */
/*
* Store the address of lzma_crc64_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_crc64_table@GOT(%ebx), %ebx
/* Complement the initial value. */
notl %eax
notl %edx
.L_align:
/*
* Check if there is enough input to use slicing-by-four.
* We need eight bytes, because the loop pre-reads four bytes.
*/
cmpl $8, %edi
jl .L_rest
/* Check if we have reached alignment of four bytes. */
testl $3, %esi
jz .L_slice
/* Calculate CRC of the next input byte. */
movzbl (%esi), %ebp
incl %esi
movzbl %al, %ecx
xorl %ecx, %ebp
shrdl $8, %edx, %eax
xorl (%ebx, %ebp, 8), %eax
shrl $8, %edx
xorl 4(%ebx, %ebp, 8), %edx
decl %edi
jmp .L_align
.L_slice:
/*
* If we get here, there's at least eight bytes of aligned input
* available. Make %edi multiple of four bytes. Store the possible
* remainder over the "size" variable in the argument stack.
*/
movl %edi, 0x18(%esp)
andl $-4, %edi
subl %edi, 0x18(%esp)
/*
* Let %edi be buf + size - 4 while running the main loop. This way
* we can compare for equality to determine when exit the loop.
*/
addl %esi, %edi
subl $4, %edi
/* Read in the first four aligned bytes. */
movl (%esi), %ecx
.L_loop:
xorl %eax, %ecx
movzbl %cl, %ebp
movl 0x1800(%ebx, %ebp, 8), %eax
xorl %edx, %eax
movl 0x1804(%ebx, %ebp, 8), %edx
movzbl %ch, %ebp
xorl 0x1000(%ebx, %ebp, 8), %eax
xorl 0x1004(%ebx, %ebp, 8), %edx
shrl $16, %ecx
movzbl %cl, %ebp
xorl 0x0800(%ebx, %ebp, 8), %eax
xorl 0x0804(%ebx, %ebp, 8), %edx
movzbl %ch, %ebp
addl $4, %esi
xorl (%ebx, %ebp, 8), %eax
xorl 4(%ebx, %ebp, 8), %edx
/* Check for end of aligned input. */
cmpl %edi, %esi
/*
* Copy the next input byte to %ecx. It is slightly faster to
* read it here than at the top of the loop.
*/
movl (%esi), %ecx
jl .L_loop
/*
* Process the remaining four bytes, which we have already
* copied to %ecx.
*/
xorl %eax, %ecx
movzbl %cl, %ebp
movl 0x1800(%ebx, %ebp, 8), %eax
xorl %edx, %eax
movl 0x1804(%ebx, %ebp, 8), %edx
movzbl %ch, %ebp
xorl 0x1000(%ebx, %ebp, 8), %eax
xorl 0x1004(%ebx, %ebp, 8), %edx
shrl $16, %ecx
movzbl %cl, %ebp
xorl 0x0800(%ebx, %ebp, 8), %eax
xorl 0x0804(%ebx, %ebp, 8), %edx
movzbl %ch, %ebp
addl $4, %esi
xorl (%ebx, %ebp, 8), %eax
xorl 4(%ebx, %ebp, 8), %edx
/* 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
shrdl $8, %edx, %eax
xorl (%ebx, %ebp, 8), %eax
shrl $8, %edx
xorl 4(%ebx, %ebp, 8), %edx
decl %edi
jmp .L_rest
.L_return:
/* Complement the final value. */
notl %eax
notl %edx
popl %ebp
popl %edi
popl %esi
popl %ebx
ret
.size lzma_crc64, .-lzma_crc64
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