| /* |
| * Round a number upwards to a prime (not usually the nearest one). |
| * |
| * Uses a table of successive 32-bit primes whose ratio is roughly |
| * constant. This keeps the relative upwards 'rounding error' bounded |
| * and the data size small. A simple 'predict-correct' compression is |
| * used to compress primes to one byte per prime. See genhashsizes.py |
| * for details. |
| * |
| * The minimum prime returned here must be coordinated with the possible |
| * probe sequence steps in duk_hobject and duk_heap stringtable. |
| */ |
| |
| #include "duk_internal.h" |
| |
| /* Awkward inclusion condition: drop out of compilation if not needed by any |
| * call site: object hash part or probing stringtable. |
| */ |
| #if defined(DUK_USE_HOBJECT_HASH_PART) || defined(DUK_USE_STRTAB_PROBE) |
| |
| /* hash size ratio goal, must match genhashsizes.py */ |
| #define DUK__HASH_SIZE_RATIO 1177 /* floor(1.15 * (1 << 10)) */ |
| |
| /* prediction corrections for prime list (see genhashsizes.py) */ |
| DUK_LOCAL const duk_int8_t duk__hash_size_corrections[] = { |
| 17, /* minimum prime */ |
| 4, 3, 4, 1, 4, 1, 1, 2, 2, 2, 2, 1, 6, 6, 9, 5, 1, 2, 2, 5, 1, 3, 3, 3, |
| 5, 4, 4, 2, 4, 8, 3, 4, 23, 2, 4, 7, 8, 11, 2, 12, 15, 10, 1, 1, 5, 1, 5, |
| 8, 9, 17, 14, 10, 7, 5, 2, 46, 21, 1, 9, 9, 4, 4, 10, 23, 36, 6, 20, 29, |
| 18, 6, 19, 21, 16, 11, 5, 5, 48, 9, 1, 39, 14, 8, 4, 29, 9, 1, 15, 48, 12, |
| 22, 6, 15, 27, 4, 2, 17, 28, 8, 9, 4, 5, 8, 3, 3, 8, 37, 11, 15, 8, 30, |
| 43, 6, 33, 41, 5, 20, 32, 41, 38, 24, 77, 14, 19, 11, 4, 35, 18, 19, 41, |
| 10, 23, 16, 9, 2, |
| -1 |
| }; |
| |
| /* probe steps (see genhashsizes.py), currently assumed to be 32 entries long |
| * (DUK_UTIL_GET_HASH_PROBE_STEP macro). |
| */ |
| DUK_INTERNAL duk_uint8_t duk_util_probe_steps[32] = { |
| 2, 3, 5, 7, 11, 13, 19, 31, 41, 47, 59, 67, 73, 79, 89, 101, 103, 107, |
| 109, 127, 137, 139, 149, 157, 163, 167, 173, 181, 191, 193, 197, 199 |
| }; |
| |
| DUK_INTERNAL duk_uint32_t duk_util_get_hash_prime(duk_uint32_t size) { |
| const duk_int8_t *p = duk__hash_size_corrections; |
| duk_uint32_t curr; |
| |
| curr = (duk_uint32_t) *p++; |
| for (;;) { |
| duk_small_int_t t = (duk_small_int_t) *p++; |
| if (t < 0) { |
| /* may happen if size is very close to 2^32-1 */ |
| break; |
| } |
| |
| /* prediction: portable variant using doubles if 64-bit values not available */ |
| #ifdef DUK_USE_64BIT_OPS |
| curr = (duk_uint32_t) ((((duk_uint64_t) curr) * ((duk_uint64_t) DUK__HASH_SIZE_RATIO)) >> 10); |
| #else |
| /* 32-bit x 11-bit = 43-bit, fits accurately into a double */ |
| curr = (duk_uint32_t) DUK_FLOOR(((double) curr) * ((double) DUK__HASH_SIZE_RATIO) / 1024.0); |
| #endif |
| |
| /* correction */ |
| curr += t; |
| |
| DUK_DDD(DUK_DDDPRINT("size=%ld, curr=%ld", (long) size, (long) curr)); |
| |
| if (curr >= size) { |
| return curr; |
| } |
| } |
| return 0; |
| } |
| |
| #endif /* DUK_USE_HOBJECT_HASH_PART || DUK_USE_STRTAB_PROBE */ |
