241 lines
6.6 KiB
NASM
241 lines
6.6 KiB
NASM
; crc32.asm -- compute the CRC-32 of a data stream
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; Copyright (C) 1995-2006, 2010, 2011, 2012 Mark Adler
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; For conditions of distribution and use, see copyright notice in zlib.inc
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; Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
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; CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
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; tables for updating the shift register in one step with three exclusive-ors
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; instead of four steps with four exclusive-ors. This results in about a
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; factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
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; Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
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; protection on the static variables used to control the first-use generation
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; of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
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; first call get_crc_table() to initialize the tables before allowing more than
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; one thread to use crc32().
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; Definitions for doing the crc four data bytes at a time.
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TBLS equ 1
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if DYNAMIC_CRC_TABLE eq 1
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align 4
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crc_table_empty dd 1
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;align 4
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;crc_table rd TBLS*256
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; Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
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; x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
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; Polynomials over GF(2) are represented in binary, one bit per coefficient,
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; with the lowest powers in the most significant bit. Then adding polynomials
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; is just exclusive-or, and multiplying a polynomial by x is a right shift by
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; one. If we call the above polynomial p, and represent a byte as the
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; polynomial q, also with the lowest power in the most significant bit (so the
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; byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
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; where a mod b means the remainder after dividing a by b.
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; This calculation is done using the shift-register method of multiplying and
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; taking the remainder. The register is initialized to zero, and for each
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; incoming bit, x^32 is added mod p to the register if the bit is a one (where
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; x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
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; x (which is shifting right by one and adding x^32 mod p if the bit shifted
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; out is a one). We start with the highest power (least significant bit) of
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; q and repeat for all eight bits of q.
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; The first table is simply the CRC of all possible eight bit values. This is
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; all the information needed to generate CRCs on data a byte at a time for all
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; combinations of CRC register values and incoming bytes. The remaining tables
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; allow for word-at-a-time CRC calculation for both big-endian and little-
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; endian machines, where a word is four bytes.
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;void ()
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align 4
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proc make_crc_table uses ecx edx edi
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zlib_debug 'make_crc_table'
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; generate a crc for every 8-bit value
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xor edx, edx
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mov edi, crc_table
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.1:
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mov ecx, 8
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mov eax, edx
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.2:
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shr eax, 1
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jnc @f
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xor eax, 0xEDB88320
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@@:
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loop .2
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stosd
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inc dl
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jnz .1
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mov dword[crc_table_empty],0
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ret
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endp
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else ;!DYNAMIC_CRC_TABLE
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; ========================================================================
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; Tables of CRC-32s of all single-byte values, made by make_crc_table().
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;include 'crc32.inc'
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end if ;DYNAMIC_CRC_TABLE
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; =========================================================================
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; This function can be used by asm versions of crc32()
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;const z_crc_t* ()
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align 4
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proc get_crc_table
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if DYNAMIC_CRC_TABLE eq 1
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cmp dword[crc_table_empty],0
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je @f ;if (..)
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call make_crc_table
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@@:
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end if
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mov eax,crc_table
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ret
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endp
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; =========================================================================
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;unsigned long (crc, buf, len)
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; unsigned long crc
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; unsigned char *buf
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; uInt len
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align 4
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proc calc_crc32 uses ecx esi, p1crc:dword, buf:dword, len:dword
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xor eax,eax
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mov esi,[buf]
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zlib_debug 'calc_crc32 buf = %d',esi
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cmp esi,Z_NULL
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je .end_f ;if (..==0) return 0
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if DYNAMIC_CRC_TABLE eq 1
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cmp dword[crc_table_empty],0
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je @f ;if (..)
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call make_crc_table
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@@:
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end if
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mov eax,[p1crc]
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mov ecx,[len]
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call crc
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.end_f:
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ret
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endp
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GF2_DIM equ 32 ;dimension of GF(2) vectors (length of CRC)
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; =========================================================================
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;unsigned long (mat, vec)
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; unsigned long *mat
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; unsigned long vec
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align 4
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proc gf2_matrix_times, mat:dword, vec:dword
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; unsigned long sum;
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; sum = 0;
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; while (vec) {
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; if (vec & 1)
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; sum ^= *mat;
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; vec >>= 1;
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; mat++;
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; }
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; return sum;
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ret
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endp
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; =========================================================================
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;local void (square, mat)
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; unsigned long *square
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; unsigned long *mat
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align 4
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proc gf2_matrix_square, square:dword, mat:dword
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; int n;
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; for (n = 0; n < GF2_DIM; n++)
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; square[n] = gf2_matrix_times(mat, mat[n]);
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ret
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endp
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; =========================================================================
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;uLong (crc1, crc2, len2)
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; uLong crc1
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; uLong crc2
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; z_off64_t len2
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align 4
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proc crc32_combine_, crc1:dword, crc2:dword, len2:dword
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; int n;
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; unsigned long row;
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; unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
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; unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
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; degenerate case (also disallow negative lengths)
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; if (len2 <= 0)
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; return crc1;
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; put operator for one zero bit in odd
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; odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
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; row = 1;
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; for (n = 1; n < GF2_DIM; n++) {
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; odd[n] = row;
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; row <<= 1;
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; }
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; put operator for two zero bits in even
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; gf2_matrix_square(even, odd);
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; put operator for four zero bits in odd
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; gf2_matrix_square(odd, even);
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; apply len2 zeros to crc1 (first square will put the operator for one
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; zero byte, eight zero bits, in even)
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; do {
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; apply zeros operator for this bit of len2
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; gf2_matrix_square(even, odd);
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; if (len2 & 1)
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; crc1 = gf2_matrix_times(even, crc1);
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; len2 >>= 1;
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; if no more bits set, then done
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; if (len2 == 0)
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; break;
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; another iteration of the loop with odd and even swapped
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; gf2_matrix_square(odd, even);
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; if (len2 & 1)
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; crc1 = gf2_matrix_times(odd, crc1);
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; len2 >>= 1;
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; if no more bits set, then done
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; } while (len2 != 0);
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; return combined crc
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; crc1 ^= crc2;
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; return crc1;
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ret
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endp
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; =========================================================================
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;uLong (crc1, crc2, len2)
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; uLong crc1
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; uLong crc2
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; z_off_t len2
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align 4
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proc crc32_combine, crc1:dword, crc2:dword, len2:dword
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stdcall crc32_combine_, [crc1], [crc2], [len2]
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ret
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endp
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;uLong (crc1, crc2, len2)
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; uLong crc1
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; uLong crc2
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; z_off64_t len2
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align 4
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proc crc32_combine64, crc1:dword, crc2:dword, len2:dword
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stdcall crc32_combine_, [crc1], [crc2], [len2]
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ret
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endp
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