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author | wm4 <wm4@nowhere> | 2019-10-31 13:16:58 +0100 |
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committer | wm4 <wm4@nowhere> | 2019-10-31 13:16:58 +0100 |
commit | 7510ed6f684041db643c051cb17b13abf663b3b2 (patch) | |
tree | e99355085b8f9ccb13d883d08dc22dca1a58ff50 /common | |
parent | 6d92e5550203b04b7254eb8ffe31734e57070d79 (diff) | |
download | mpv-7510ed6f684041db643c051cb17b13abf663b3b2.tar.bz2 mpv-7510ed6f684041db643c051cb17b13abf663b3b2.tar.xz |
common: add mp_log2()
To be used in the next commit.
According to compiler explorer, __builtin_clz is very widely available,
and it barely makes sense to provide a fallback. clang also eats this
(and identifies at least as GCC 4). Actually, there's doubt that a fast
log2 implementation is needed at all (I guess UTF-8 parsing needs it,
but something UTF-8-specific would probably make it faster than using
log2). So the fallback is just something naive.
Diffstat (limited to 'common')
-rw-r--r-- | common/common.c | 18 | ||||
-rw-r--r-- | common/common.h | 2 |
2 files changed, 20 insertions, 0 deletions
diff --git a/common/common.c b/common/common.c index d0b2382b78..967ab961c0 100644 --- a/common/common.c +++ b/common/common.c @@ -318,3 +318,21 @@ char **mp_dup_str_array(void *tctx, char **s) MP_TARRAY_APPEND(tctx, r, num_r, NULL); return r; } + +// Return rounded down integer log 2 of v, i.e. position of highest set bit. +// mp_log2(0) == 0 +// mp_log2(1) == 0 +// mp_log2(31) == 4 +// mp_log2(32) == 5 +unsigned int mp_log2(uint32_t v) +{ +#if defined(__GNUC__) && __GNUC__ >= 4 + return v ? 31 - __builtin_clz(v) : 0; +#else + for (int x = 31; x >= 0; x--) { + if (v & (((uint32_t)1) << x)) + return x; + } + return 0; +#endif +} diff --git a/common/common.h b/common/common.h index 16e1ec4cfd..5e6950c931 100644 --- a/common/common.h +++ b/common/common.h @@ -88,6 +88,8 @@ bool mp_rect_intersection(struct mp_rect *rc, const struct mp_rect *rc2); bool mp_rect_contains(struct mp_rect *rc, int x, int y); bool mp_rect_equals(struct mp_rect *rc1, struct mp_rect *rc2); +unsigned int mp_log2(uint32_t v); + int mp_snprintf_cat(char *str, size_t size, const char *format, ...) PRINTF_ATTRIBUTE(3, 4); |