On Sun, 5 Jan 2025 02:50:34 GMT, j3graham <d...@openjdk.org> wrote: > > 2. The leading zero scenario is not common, and there is no need to > > optimize this scenario. > > Another approach would be to limit the “fast” path to the case where the > overall string length is 9 or less. That would allow overflow-free > calculation without the extra bytecode weight of skipping leading zeros, > possibly still with simpler code.
If we want to reach the fastest limit, we need to construct a cache array DIGITS for decimal integers, such as this: https://github.com/wenshao/jdk/tree/refs/heads/optim_parse_int_long_202501_x1 ( commit https://github.com/wenshao/jdk/commit/c2e2c7e8fe8cd662db97d713f4043622de21f1d0 ) @Stable private static final byte[] DECIMAL_DIGITS = new byte[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, ... // 256 }; static int digit(byte ch) { return DECIMAL_DIGITS[ch & 0xFF]; } public static int parseInt(String s, int radix) // ... ... int result = 0, d0, d1; boolean inRange; byte firstChar = value[0]; if (firstChar != '-' && firstChar != '+') { if (inRange = ((d0 = digit(firstChar)) != -1)) { result = -d0; } } else { inRange = len != 1; } int limit = MIN_VALUE + (firstChar != '-' ? 1 : 0); int i = 1; while (inRange && i + 1 < len && (d0 = digit(value[i ])) != -1 && (d1 = digit(value[i + 1])) != -1 ) { d1 = d0 * 10 + d1; // max digits is 19, no need to check inRange (result == MULT_MIN_100 && digit <= (MULT_MIN_100 * 100 - limit)) if (inRange = (result >= MULT_MIN_100)) { result = result * 100 - d1; i += 2; } } if (inRange && result <= 0) { if (i + 1 == len && (d0 = digit(value[i])) != -1) { if (result > MULT_MIN_10 || (result == MULT_MIN_10 && d0 <= (MULT_MIN_10 * 10 - limit))) { result = result * 10 - d0; i++; } } if (i == len) { return firstChar != '-' ? -result : result; } } throw NumberFormatException.forInputString(s); } This will be faster, but there may be cache misses in some cases and performance will decrease. ------------- PR Comment: https://git.openjdk.org/jdk/pull/22919#issuecomment-2571517185
