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lib: Fix log2_ceil() for 0xffffffff

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Current log2_ceil(x) is defined as log2(x * 2 - 1). When x is larger
than (1 << 31), (x * 2 - 1) won't fit in u32, leading to incorrect
result. Therefore, correct it as (log2(x - 1) + 1). Also add unit tests
for inline functions in lib.h.

BUG=none
TEST=make tests/lib/lib-test
BRANCH=none

Change-Id: If868f793b909a6ad7fc48a7affac15e2c714fa2e
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59834
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
This commit is contained in:
Yu-Ping Wu
2021-12-02 10:54:32 +08:00
committed by Felix Held
parent 04cf42775c
commit 00c834dc26
3 changed files with 65 additions and 2 deletions
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4
src/include/lib.h
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@@ -54,8 +54,8 @@ static inline int log2(u32 x) { return sizeof(x) * 8 - clz(x) - 1; }
/* Find First Set: __ffs(1) == 0, __ffs(0) == -1, __ffs(1<<31) == 31 */
static inline int __ffs(u32 x) { return log2(x & (u32)(-(s32)x)); }
/* Integer binary logarithm (rounding up): log2_ceil(0) == -1, log2(5) == 3 */
static inline int log2_ceil(u32 x) { return (x == 0) ? -1 : log2(x * 2 - 1); }
/* Integer binary logarithm (rounding up): log2_ceil(0) == -1, log2_ceil(5) == 3 */
static inline int log2_ceil(u32 x) { return (x == 0) ? -1 : log2(x - 1) + 1; }
static inline int popcnt64(u64 x) { return __builtin_popcountll(x); }
static inline int clz64(u64 x) { return x ? __builtin_clzll(x) : sizeof(x) * 8; }