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| author | Kaz Kylheku <kaz@kylheku.com> | 2019-02-19 06:39:02 -0800 |
|---|---|---|
| committer | Kaz Kylheku <kaz@kylheku.com> | 2019-02-19 06:39:02 -0800 |
| commit | 15b7c542dc44899e8db7addfcc2f1c1c4a188b49 (patch) | |
| tree | 3857de5f06aae8f5bf25acebe306920545fc7ee4 /arith.c | |
| parent | 2b3179ea5e50778f1f19054b9d6d8aa06d683081 (diff) | |
| download | txr-15b7c542dc44899e8db7addfcc2f1c1c4a188b49.tar.gz txr-15b7c542dc44899e8db7addfcc2f1c1c4a188b49.tar.bz2 txr-15b7c542dc44899e8db7addfcc2f1c1c4a188b49.zip | |
mpi/arith: optimize "highest bit" with GCC builtins.
* arith.c (highest_bit): On GCC, use __builtin_clz.
* mpi/mpi.c (s_highest_bit): Likewise.
Diffstat (limited to 'arith.c')
| -rw-r--r-- | arith.c | 8 |
1 files changed, 7 insertions, 1 deletions
@@ -268,7 +268,13 @@ val bignum_len(val num) int highest_bit(int_ptr_t n) { -#if CHAR_BIT * SIZEOF_PTR == 64 +#if defined __GNUC__ && SIZEOF_PTR == SIZEOF_INT + return (n == 0) ? 0 : (CHAR_BIT * SIZEOF_PTR - __builtin_clz(n)); +#elif defined __GNUC__ && SIZEOF_PTR == SIZEOF_LONG + return (n == 0) ? 0 : (CHAR_BIT * SIZEOF_PTR - __builtin_clzl(n)); +#elif defined __GNUC__ && SIZEOF_PTR == SIZEOF_LONGLONG_T + return (n == 0) ? 0 : (CHAR_BIT * SIZEOF_PTR - __builtin_clzll(n)); +#elif CHAR_BIT * SIZEOF_PTR == 64 if (n & 0x7FFFFFFF00000000) { if (n & 0x7FFF000000000000) { if (n & 0x7F00000000000000) { |