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shared: add ALIGN_POWER2 macro

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Sounds easy, turns out to be horrible to implement: ALIGN_POWER2 returns
the next higher power of 2. clz(0) is undefined, same is true for
left-shift-overflows, yey, C rocks!
This commit is contained in:
David Herrmann 2014-05-13 19:47:58 +02:00
parent ead349509e
commit 625e870b4f
2 changed files with 44 additions and 0 deletions
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13
src/shared/macro.h
View file

@ -100,6 +100,19 @@ static inline size_t ALIGN_TO(size_t l, size_t ali) {
#define ALIGN_TO_PTR(p, ali) ((void*) ALIGN_TO((unsigned long) p, ali))
/* align to next higher power-of-2 (except for: 0 => 0, overflow => 0) */
static inline unsigned long ALIGN_POWER2(unsigned long u) {
/* clz(0) is undefined */
if (u == 1)
return 1;
/* left-shift overflow is undefined */
if (__builtin_clzl(u - 1UL) < 1)
return 0;
return 1UL << (sizeof(u) * 8 - __builtin_clzl(u - 1UL));
}
#define ELEMENTSOF(x) (sizeof(x)/sizeof((x)[0]))
/*

31
src/test/test-util.c
View file

@ -37,6 +37,36 @@ static void test_streq_ptr(void) {
assert_se(!streq_ptr("abc", "cdef"));
}
static void test_align_power2(void) {
unsigned long i, p2;
assert_se(ALIGN_POWER2(0) == 0);
assert_se(ALIGN_POWER2(1) == 1);
assert_se(ALIGN_POWER2(2) == 2);
assert_se(ALIGN_POWER2(3) == 4);
assert_se(ALIGN_POWER2(12) == 16);
assert_se(ALIGN_POWER2(ULONG_MAX) == 0);
assert_se(ALIGN_POWER2(ULONG_MAX - 1) == 0);
assert_se(ALIGN_POWER2(ULONG_MAX - 1024) == 0);
assert_se(ALIGN_POWER2(ULONG_MAX / 2) == ULONG_MAX / 2 + 1);
assert_se(ALIGN_POWER2(ULONG_MAX + 1) == 0);
for (i = 1; i < 131071; ++i) {
for (p2 = 1; p2 < i; p2 <<= 1)
/* empty */ ;
assert_se(ALIGN_POWER2(i) == p2);
}
for (i = ULONG_MAX - 1024; i < ULONG_MAX; ++i) {
for (p2 = 1; p2 && p2 < i; p2 <<= 1)
/* empty */ ;
assert_se(ALIGN_POWER2(i) == p2);
}
}
static void test_first_word(void) {
assert_se(first_word("Hello", ""));
assert_se(first_word("Hello", "Hello"));
@ -680,6 +710,7 @@ int main(int argc, char *argv[]) {
log_open();
test_streq_ptr();
test_align_power2();
test_first_word();
test_close_many();
test_parse_boolean();