basic/logarithm: add popcount() wrapper

__builtin_popcount() is a bit of a mouthful, so let's provide a helper. Using _Generic has the advantage that if a type other then the ones on the list is given, compilation will fail. This is nice, because if by any change we pass a wider type, it is rejected immediately instead of being truncated. log.h is also needed. It is included transitively, but let's include it directly. macro.h is *not* needed.
2023-04-24 10:02:30 +02:00
parent 6eccc3cfa9
commit a12bc99ef0
4 changed files with 37 additions and 7 deletions
@@ -1,53 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-#pragma once
-
-#include <stdint.h>
-
-#include "macro.h"
-
-/* Note: log2(0) == log2(1) == 0 here and below. */
-
-#define CONST_LOG2ULL(x) ((x) > 1 ? (unsigned) __builtin_clzll(x) ^ 63U : 0)
-#define NONCONST_LOG2ULL(x) ({                                     \
-                unsigned long long _x = (x);                       \
-                _x > 1 ? (unsigned) __builtin_clzll(_x) ^ 63U : 0; \
-        })
-#define LOG2ULL(x) __builtin_choose_expr(__builtin_constant_p(x), CONST_LOG2ULL(x), NONCONST_LOG2ULL(x))
-
-static inline unsigned log2u64(uint64_t x) {
-#if __SIZEOF_LONG_LONG__ == 8
-        return LOG2ULL(x);
-#else
-#  error "Wut?"
-#endif
-}
-
-static inline unsigned u32ctz(uint32_t n) {
-#if __SIZEOF_INT__ == 4
-        return n != 0 ? __builtin_ctz(n) : 32;
-#else
-#  error "Wut?"
-#endif
-}
-
-#define CONST_LOG2U(x) ((x) > 1 ? __SIZEOF_INT__ * 8 - __builtin_clz(x) - 1 : 0)
-#define NONCONST_LOG2U(x) ({                                             \
-                unsigned _x = (x);                                       \
-                _x > 1 ? __SIZEOF_INT__ * 8 - __builtin_clz(_x) - 1 : 0; \
-        })
-#define LOG2U(x) __builtin_choose_expr(__builtin_constant_p(x), CONST_LOG2U(x), NONCONST_LOG2U(x))
-
-static inline unsigned log2i(int x) {
-        return LOG2U(x);
-}
-
-static inline unsigned log2u(unsigned x) {
-        return LOG2U(x);
-}
-
-static inline unsigned log2u_round_up(unsigned x) {
-        if (x <= 1)
-                return 0;
-
-        return log2u(x - 1) + 1;
-}