#ifdef DYNAMIC_CRC_TABLE
-local volatile int crc_table_empty = 1;
local z_crc_t FAR crc_table[256];
local z_crc_t FAR x2n_table[32];
local void make_crc_table OF((void));
local void write_table64 OF((FILE *, const z_word_t FAR *, int));
#endif /* MAKECRCH */
+/*
+ Define a once() function depending on the availability of atomics. If this is
+ compiled with DYNAMIC_CRC_TABLE defined, and if CRCs will be computed in
+ multiple threads, and if atomics are not available, then get_crc_table() must
+ be called to initialize the tables and must return before any threads are
+ allowed to compute or combine CRCs.
+ */
+
+/* Definition of once functionality. */
+typedef struct once_s once_t;
+local void once OF((once_t *, void (*)(void)));
+
+/* Check for the availability of atomics. */
+#if defined(__STDC__) && __STDC_VERSION__ >= 201112L && \
+ !defined(__STDC_NO_ATOMICS__)
+
+#include <stdatomic.h>
+
+/* Structure for once(), which must be initialized with ONCE_INIT. */
+struct once_s {
+ atomic_flag begun;
+ atomic_int done;
+};
+#define ONCE_INIT {ATOMIC_FLAG_INIT, 0}
+
+/*
+ Run the provided init() function exactly once, even if multiple threads
+ invoke once() at the same time. The state must be a once_t initialized with
+ ONCE_INIT.
+ */
+local void once(state, init)
+ once_t *state;
+ void (*init)(void);
+{
+ if (!atomic_load(&state->done)) {
+ if (atomic_flag_test_and_set(&state->begun))
+ while (!atomic_load(&state->done))
+ ;
+ else {
+ init();
+ atomic_store(&state->done, 1);
+ }
+ }
+}
+
+#else /* no atomics */
+
+/* Structure for once(), which must be initialized with ONCE_INIT. */
+struct once_s {
+ volatile int begun;
+ volatile int done;
+};
+#define ONCE_INIT {0, 0}
+
+/* Test and set. Alas, not atomic, but tries to minimize the period of
+ vulnerability. */
+local int test_and_set OF((int volatile *));
+local int test_and_set(flag)
+ int volatile *flag;
+{
+ int was;
+
+ was = *flag;
+ *flag = 1;
+ return was;
+}
+
+/* Run the provided init() function once. This is not thread-safe. */
+local void once(state, init)
+ once_t *state;
+ void (*init)(void);
+{
+ if (!state->done) {
+ if (test_and_set(&state->begun))
+ while (!state->done)
+ ;
+ else {
+ init();
+ state->done = 1;
+ }
+ }
+}
+
+#endif
+
+/* State for once(). */
+local once_t made = ONCE_INIT;
+
/*
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.
local void make_crc_table()
{
+ unsigned i, j, n;
z_crc_t p;
- static volatile int first = 1; /* flag to limit concurrent making */
-
- /* 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) {
- unsigned i, j, n;
- first = 0;
-
- /* initialize the CRC of bytes tables */
- for (i = 0; i < 256; i++) {
- p = i;
- for (j = 0; j < 8; j++)
- p = p & 1 ? (p >> 1) ^ POLY : p >> 1;
- crc_table[i] = p;
+
+ /* initialize the CRC of bytes tables */
+ for (i = 0; i < 256; i++) {
+ p = i;
+ for (j = 0; j < 8; j++)
+ p = p & 1 ? (p >> 1) ^ POLY : p >> 1;
+ crc_table[i] = p;
#ifdef W
- crc_big_table[i] = byte_swap(p);
+ crc_big_table[i] = byte_swap(p);
#endif
- }
+ }
+
+ /* initialize the x^2^n mod p(x) table */
+ p = (z_crc_t)1 << 30; /* x^1 */
+ x2n_table[0] = p;
+ for (n = 1; n < 32; n++)
+ x2n_table[n] = p = multmodp(p, p);
- /* initialize the x^2^n mod p(x) table */
- p = (z_crc_t)1 << 30; /* x^1 */
- x2n_table[0] = p;
- for (n = 1; n < 32; n++)
- x2n_table[n] = p = multmodp(p, p);
#ifdef W
- /* initialize the braiding tables -- needs x2n_table[] */
- braid(crc_braid_table, crc_braid_big_table, N, W);
+ /* initialize the braiding tables -- needs x2n_table[] */
+ braid(crc_braid_table, crc_braid_big_table, N, W);
#endif
- /* 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
{
/*
}
/*
- Return x^(n+k) modulo p(x). Requires that x2n_table[] has been initialized.
+ Return x^(n * 2^k) modulo p(x). Requires that x2n_table[] has been
+ initialized.
*/
local z_crc_t x2nmodp(n, k)
z_off64_t n;
#endif /* W */
/* =========================================================================
- * This function can be used by asm versions of crc32()
+ * This function can be used by asm versions of crc32(), and to force the
+ * generation of the CRC tables in a threaded application.
*/
const z_crc_t FAR * ZEXPORT get_crc_table()
{
#ifdef DYNAMIC_CRC_TABLE
- if (crc_table_empty)
- make_crc_table();
+ once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */
return (const z_crc_t FAR *)crc_table;
}
+/* =========================================================================
+ * Use ARM machine instructions if available. This will compute the CRC about
+ * ten times faster than the braided calculation. This code does not check for
+ * the presence of the CRC instruction at run time. __ARM_FEATURE_CRC32 will
+ * only be defined if the compilation specifies an ARM processor architecture
+ * that has the instructions. For example, compiling with -march=armv8.1-a or
+ * -march=armv8-a+crc, or -march=native if the compile machine has the crc32
+ * instructions.
+ */
+#if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32) && W == 8
+
+/*
+ Constants empirically determined to maximize speed. These values are from
+ measurements on a Cortex-A57. Your mileage may vary.
+ */
+#define Z_BATCH 3990 /* number of words in a batch */
+#define Z_BATCH_ZEROS 0xa10d3d0c /* computed from Z_BATCH = 3990 */
+#define Z_BATCH_MIN 800 /* fewest words in a final batch */
+
+unsigned long ZEXPORT crc32_z(crc, buf, len)
+ unsigned long crc;
+ const unsigned char FAR *buf;
+ z_size_t len;
+{
+ z_crc_t val;
+ z_word_t crc1, crc2;
+ const z_word_t *word;
+ z_word_t val0, val1, val2;
+ z_size_t last, last2, i;
+ z_size_t num;
+
+ /* Return initial CRC, if requested. */
+ if (buf == Z_NULL) return 0;
+
+#ifdef DYNAMIC_CRC_TABLE
+ once(&made, make_crc_table);
+#endif /* DYNAMIC_CRC_TABLE */
+
+ /* Pre-condition the CRC */
+ crc ^= 0xffffffff;
+
+ /* Compute the CRC up to a word boundary. */
+ while (len && ((z_size_t)buf & 7) != 0) {
+ len--;
+ val = *buf++;
+ __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
+ }
+
+ /* Prepare to compute the CRC on full 64-bit words word[0..num-1]. */
+ word = (z_word_t const *)buf;
+ num = len >> 3;
+ len &= 7;
+
+ /* Do three interleaved CRCs to realize the throughput of one crc32x
+ instruction per cycle. Each CRC is calcuated on Z_BATCH words. The three
+ CRCs are combined into a single CRC after each set of batches. */
+ while (num >= 3 * Z_BATCH) {
+ crc1 = 0;
+ crc2 = 0;
+ for (i = 0; i < Z_BATCH; i++) {
+ val0 = word[i];
+ val1 = word[i + Z_BATCH];
+ val2 = word[i + 2 * Z_BATCH];
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
+ }
+ word += 3 * Z_BATCH;
+ num -= 3 * Z_BATCH;
+ crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc1;
+ crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc2;
+ }
+
+ /* Do one last smaller batch with the remaining words, if there are enough
+ to pay for the combination of CRCs. */
+ last = num / 3;
+ if (last >= Z_BATCH_MIN) {
+ last2 = last << 1;
+ crc1 = 0;
+ crc2 = 0;
+ for (i = 0; i < last; i++) {
+ val0 = word[i];
+ val1 = word[i + last];
+ val2 = word[i + last2];
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
+ }
+ word += 3 * last;
+ num -= 3 * last;
+ val = x2nmodp(last, 6);
+ crc = multmodp(val, crc) ^ crc1;
+ crc = multmodp(val, crc) ^ crc2;
+ }
+
+ /* Compute the CRC on any remaining words. */
+ for (i = 0; i < num; i++) {
+ val0 = word[i];
+ __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
+ }
+ word += num;
+
+ /* Complete the CRC on any remaining bytes. */
+ buf = (const unsigned char FAR *)word;
+ while (len) {
+ len--;
+ val = *buf++;
+ __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
+ }
+
+ /* Return the CRC, post-conditioned. */
+ return crc ^ 0xffffffff;
+}
+
+#else
+
/* ========================================================================= */
unsigned long ZEXPORT crc32_z(crc, buf, len)
unsigned long crc;
if (buf == Z_NULL) return 0;
#ifdef DYNAMIC_CRC_TABLE
- if (crc_table_empty)
- make_crc_table();
+ once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */
/* Pre-condition the CRC */
return crc ^ 0xffffffff;
}
+#endif
+
/* ========================================================================= */
unsigned long ZEXPORT crc32(crc, buf, len)
unsigned long crc;
z_off64_t len2;
{
#ifdef DYNAMIC_CRC_TABLE
- if (crc_table_empty)
- make_crc_table();
+ once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */
return multmodp(x2nmodp(len2, 3), crc1) ^ crc2;
}
z_off64_t len2;
{
#ifdef DYNAMIC_CRC_TABLE
- if (crc_table_empty)
- make_crc_table();
+ once(&made, make_crc_table);
#endif /* DYNAMIC_CRC_TABLE */
return x2nmodp(len2, 3);
}
projects / zlib.git / blobdiff