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Split crc table generating code (MAKECRCH) out into separate tool mak…
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…ecrct.
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@Dead2
Dead2 committed Sep 20, 2019
1 parent 8dd3bb2 commit 1e424d9
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Showing 4 changed files with 204 additions and 213 deletions.
3 changes: 3 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -860,6 +860,9 @@ if (ZLIB_ENABLE_TESTS)
add_executable(maketrees tools/maketrees.c trees.c)
target_include_directories(maketrees PUBLIC ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR})

add_executable(makecrct tools/makecrct.c)
target_include_directories(makecrct PUBLIC ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR})

if(HAVE_OFF64_T)
add_executable(example64 test/example.c)
configure_test_executable(example64)
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13 changes: 11 additions & 2 deletions Makefile.in
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Expand Up @@ -85,7 +85,7 @@ PIC_OBJS = $(PIC_OBJC)

all: static shared

static: example$(EXE) minigzip$(EXE) fuzzers makefixed$(EXE) maketrees$(EXE)
static: example$(EXE) minigzip$(EXE) fuzzers makefixed$(EXE) maketrees$(EXE) makecrct$(EXE)

shared: examplesh$(EXE) minigzipsh$(EXE)

Expand Down Expand Up @@ -199,6 +199,9 @@ makefixed.o:
maketrees.o:
$(CC) $(CFLAGS) $(INCLUDES) -c -o $@ $(SRCDIR)/tools/maketrees.c

makecrct.o:
$(CC) $(CFLAGS) $(INCLUDES) -c -o $@ $(SRCDIR)/tools/makecrct.c

zlibrc.o: win32/zlib$(SUFFIX)1.rc
$(RC) $(RCFLAGS) -o $@ win32/zlib$(SUFFIX)1.rc

Expand Down Expand Up @@ -274,6 +277,12 @@ ifneq ($(STRIP),)
$(STRIP) $@
endif

makecrct$(EXE): makecrct.o $(OBJG) $(STATICLIB)
$(CC) $(LDFLAGS) -o $@ makecrct.o $(OBJG) $(TEST_LIBS) $(LDSHAREDLIBC)
ifneq ($(STRIP),)
$(STRIP) $@
endif

install-shared: $(SHAREDTARGET)
ifneq ($(SHAREDTARGET),)
-@if [ ! -d $(DESTDIR)$(sharedlibdir) ]; then mkdir -p $(DESTDIR)$(sharedlibdir); fi
Expand Down Expand Up @@ -348,7 +357,7 @@ clean:
example64$(EXE) minigzip64$(EXE) \
checksum_fuzzer$(EXE) compress_fuzzer$(EXE) example_small_fuzzer$(EXE) example_large_fuzzer$(EXE) \
example_flush_fuzzer$(EXE) example_dict_fuzzer$(EXE) minigzip_fuzzer$(EXE) \
infcover makefixed$(EXE) maketrees$(EXE) \
infcover makefixed$(EXE) maketrees$(EXE) makecrct$(EXE) \
$(STATICLIB) $(IMPORTLIB) $(SHAREDLIB) $(SHAREDLIBV) $(SHAREDLIBM) \
foo.gz so_locations \
_match.s maketree
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215 changes: 4 additions & 211 deletions crc32.c
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Expand Up @@ -11,31 +11,12 @@

/* @(#) $Id$ */

# include "zbuild.h"
# include "zendian.h"
# include <inttypes.h>

/*
Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
protection on the static variables used to control the first-use generation
of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
first call get_crc_table() to initialize the tables before allowing more than
one thread to use crc32().
DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h. A main()
routine is also produced, so that this one source file can be compiled to an
executable.
*/

#ifdef MAKECRCH
# include <stdio.h>
# ifndef DYNAMIC_CRC_TABLE
# define DYNAMIC_CRC_TABLE
# endif /* !DYNAMIC_CRC_TABLE */
#endif /* MAKECRCH */

#include "zbuild.h"
#include "zendian.h"
#include <inttypes.h>
#include "deflate.h"
#include "functable.h"
#include "crc32.h"


/* Local functions for crc concatenation */
Expand All @@ -56,188 +37,10 @@ static uint32_t gf2_matrix_times(const uint32_t *mat, uint32_t vec) {
return sum;
}

#ifdef DYNAMIC_CRC_TABLE
volatile int crc_table_empty = 1;
static uint32_t crc_table[8][256];
static uint32_t crc_comb[GF2_DIM][GF2_DIM];
void make_crc_table(void);
static void gf2_matrix_square(uint32_t *square, const uint32_t *mat);
#ifdef MAKECRCH
static void write_table(FILE *, const uint32_t *, int);
#endif /* MAKECRCH */

/* ========================================================================= */
static void gf2_matrix_square(uint32_t *square, const uint32_t *mat) {
int n;

for (n = 0; n < GF2_DIM; n++)
square[n] = gf2_matrix_times(mat, mat[n]);
}

/*
Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
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.
Polynomials over GF(2) are represented in binary, one bit per coefficient,
with the lowest powers in the most significant bit. Then adding polynomials
is just exclusive-or, and multiplying a polynomial by x is a right shift by
one. If we call the above polynomial p, and represent a byte as the
polynomial q, also with the lowest power in the most significant bit (so the
byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
where a mod b means the remainder after dividing a by b.
This calculation is done using the shift-register method of multiplying and
taking the remainder. The register is initialized to zero, and for each
incoming bit, x^32 is added mod p to the register if the bit is a one (where
x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
x (which is shifting right by one and adding x^32 mod p if the bit shifted
out is a one). We start with the highest power (least significant bit) of
q and repeat for all eight bits of q.
The first table is simply the CRC of all possible eight bit values. This is
all the information needed to generate CRCs on data a byte at a time for all
combinations of CRC register values and incoming bytes. The remaining tables
allow for word-at-a-time CRC calculation for both big-endian and little-
endian machines, where a word is four bytes.
*/
void make_crc_table() {
uint32_t c;
int n, k;
uint32_t poly; /* polynomial exclusive-or pattern */
/* terms of polynomial defining this crc (except x^32): */
static volatile int first = 1; /* flag to limit concurrent making */
static const unsigned char p[] = {0, 1, 2, 4, 5, 7, 8, 10, 11, 12, 16, 22, 23, 26};

/* See if another task is already doing this (not thread-safe, but better
than nothing -- significantly reduces duration of vulnerability in
case the advice about DYNAMIC_CRC_TABLE is ignored) */
if (first) {
first = 0;

/* make exclusive-or pattern from polynomial (0xedb88320) */
poly = 0;
for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
poly |= (uint32_t)1 << (31 - p[n]);

/* generate a crc for every 8-bit value */
for (n = 0; n < 256; n++) {
c = (uint32_t)n;
for (k = 0; k < 8; k++)
c = c & 1 ? poly ^ (c >> 1) : c >> 1;
crc_table[0][n] = c;
}

/* generate crc for each value followed by one, two, and three zeros,
and then the byte reversal of those as well as the first table */
for (n = 0; n < 256; n++) {
c = crc_table[0][n];
crc_table[4][n] = ZSWAP32(c);
for (k = 1; k < 4; k++) {
c = crc_table[0][c & 0xff] ^ (c >> 8);
crc_table[k][n] = c;
crc_table[k + 4][n] = ZSWAP32(c);
}
}

/* generate zero operators table for crc32_combine() */

/* generate the operator to apply a single zero bit to a CRC -- the
first row adds the polynomial if the low bit is a 1, and the
remaining rows shift the CRC right one bit */
k = GF2_DIM - 3;
crc_comb[k][0] = 0xedb88320UL; /* CRC-32 polynomial */
uint32_t row = 1;
for (n = 1; n < GF2_DIM; n++) {
crc_comb[k][n] = row;
row <<= 1;
}

/* generate operators that apply 2, 4, and 8 zeros to a CRC, putting
the last one, the operator for one zero byte, at the 0 position */
gf2_matrix_square(crc_comb[k + 1], crc_comb[k]);
gf2_matrix_square(crc_comb[k + 2], crc_comb[k + 1]);
gf2_matrix_square(crc_comb[0], crc_comb[k + 2]);

/* generate operators for applying 2^n zero bytes to a CRC, filling out
the remainder of the table -- the operators repeat after GF2_DIM
values of n, so the table only needs GF2_DIM entries, regardless of
the size of the length being processed */
for (n = 1; n < k; n++)
gf2_matrix_square(crc_comb[n], crc_comb[n - 1]);

/* mark tables as complete, in case someone else is waiting */
crc_table_empty = 0;
} else { /* not first */
/* wait for the other guy to finish (not efficient, but rare) */
while (crc_table_empty)
{}
}
#ifdef MAKECRCH
{
FILE *out;

out = fopen("crc32.h", "w");
if (out == NULL) return;

/* write out CRC table to crc32.h */
fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
fprintf(out, "static const uint32_t ");
fprintf(out, "crc_table[8][256] =\n{\n {\n");
write_table(out, crc_table[0], 256);
for (k = 1; k < 8; k++) {
fprintf(out, " },\n {\n");
write_table(out, crc_table[k], 256);
}
fprintf(out, " }\n};\n");

/* write out zero operator table to crc32.h */
fprintf(out, "\nstatic const uint32_t ");
fprintf(out, "crc_comb[%d][%d] =\n{\n {\n", GF2_DIM, GF2_DIM);
write_table(out, crc_comb[0], GF2_DIM);
for (k = 1; k < GF2_DIM; k++) {
fprintf(out, " },\n {\n");
write_table(out, crc_comb[k], GF2_DIM);
}
fprintf(out, " }\n};\n");
fclose(out);
}
#endif /* MAKECRCH */
}

#ifdef MAKECRCH
static void write_table(FILE *out, const uint32_t *table, int k) {
int n;

for (n = 0; n < k; n++)
fprintf(out, "%s0x%08" PRIx32 "%s", n % 5 ? "" : " ",
(uint32_t)(table[n]),
n == k - 1 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
}

int main()
{
make_crc_table();
return 0;
}
#endif /* MAKECRCH */

#else /* !DYNAMIC_CRC_TABLE */
/* ========================================================================
* Tables of CRC-32s of all single-byte values, made by make_crc_table(),
* and tables of zero operator matrices for crc32_combine().
*/
#include "crc32.h"
#endif /* DYNAMIC_CRC_TABLE */

/* =========================================================================
* This function can be used by asm versions of crc32()
*/
const uint32_t * ZEXPORT PREFIX(get_crc_table)(void) {
#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
return (const uint32_t *)crc_table;
}

Expand Down Expand Up @@ -379,11 +182,6 @@ ZLIB_INTERNAL uint32_t crc32_big(uint32_t crc, const unsigned char *buf, uint64_
static uint32_t crc32_combine_(uint32_t crc1, uint32_t crc2, z_off64_t len2) {
int n;

#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */

if (len2 > 0)
/* operator for 2^n zeros repeats every GF2_DIM n values */
for (n = 0; len2; n = (n + 1) % GF2_DIM, len2 >>= 1)
Expand Down Expand Up @@ -439,11 +237,6 @@ static void crc32_combine_gen_(uint32_t *op, z_off64_t len2)
int j;
unsigned i;

#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */

/* if len2 is zero or negative, return the identity matrix */
if (len2 <= 0) {
row = 1;
Expand Down
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