Commit d3d86b17 authored by Nick Mathewson's avatar Nick Mathewson 🏃
Browse files

r12916@catbus: nickm | 2007-05-24 12:43:45 -0400

 Add math functions to round values to the nearest power of 2.  Make mempools more careful about making sure that the size of their chunks is a little less than a power of 2, not a little more.


svn:r10304
parent d0a5c4f9
......@@ -83,6 +83,7 @@ Things we'd like to do in 0.2.0.x:
- Push/pull documents as appropriate.
o Have clients know which authorities are v3 authorities, and what
their keys are.
- While we're at it, let v3 authorities have fqdns lines.
- Start caching consensus documents once authorities make them
- Start downloading and using consensus documents once caches serve them
. 104: Long and Short Router Descriptors (by Jun 1)
......
......@@ -96,6 +96,7 @@ extern INLINE double U64_TO_DBL(uint64_t x) {
#if defined(__GNUC__) && __GNUC__ >= 3
#define ATTR_NORETURN __attribute__((noreturn))
#define ATTR_PURE __attribute__((pure))
#define ATTR_CONST __attribute__((const))
#define ATTR_MALLOC __attribute__((malloc))
#define ATTR_NORETURN __attribute__((noreturn))
#define ATTR_NONNULL(x) __attribute__((nonnull x))
......@@ -108,6 +109,7 @@ extern INLINE double U64_TO_DBL(uint64_t x) {
#else
#define ATTR_NORETURN
#define ATTR_PURE
#define ATTR_CONST
#define ATTR_MALLOC
#define ATTR_NORETURN
#define ATTR_NONNULL(x)
......
......@@ -361,18 +361,24 @@ mp_pool_new(size_t item_size, size_t chunk_capacity)
/* Now we figure out how many items fit in each chunk. We need to fit at
* least 2 items per chunk. No chunk can be more than MAX_CHUNK bytes long,
* or less than MIN_CHUNK. */
/* XXXX020 Try a bit harder here: we want to be a bit less than a power of
2, not a bit over. */
if (chunk_capacity > MAX_CHUNK)
chunk_capacity = MAX_CHUNK;
if (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)
chunk_capacity = alloc_size * 2 + CHUNK_OVERHEAD;
/* Try to be around a power of 2 in size, since that's what allocators like
* handing out. 512K-1 byte is a lot better than 512K+1 byte. */
chunk_capacity = (size_t) round_to_power_of_2(chunk_capacity);
while (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)
chunk_capacity *= 2;
if (chunk_capacity < MIN_CHUNK)
chunk_capacity = MIN_CHUNK;
pool->new_chunk_capacity = (chunk_capacity-CHUNK_OVERHEAD) / alloc_size;
pool->item_alloc_size = alloc_size;
log_debug(LD_MM, "Capacity is %lu, item size is %lu, alloc size is %lu",
(unsigned long)pool->new_chunk_capacity,
(unsigned long)pool->item_alloc_size,
(unsigned long)(pool->new_chunk_capacity*pool->item_alloc_size));
return pool;
}
......
......@@ -213,6 +213,54 @@ _tor_free(void *mem)
tor_free(mem);
}
/* =====
* Math
* ===== */
/** Returns floor(log2(u64)). If u64 is 0, (incorrectly) returns 0. */
int
tor_log2(uint64_t u64)
{
int r = 0;
if (u64 >= (U64_LITERAL(1)<<32)) {
u64 >>= 32;
r = 32;
}
if (u64 >= (U64_LITERAL(1)<<16)) {
u64 >>= 16;
r += 16;
}
if (u64 >= (U64_LITERAL(1)<<8)) {
u64 >>= 8;
r += 8;
}
if (u64 >= (U64_LITERAL(1)<<4)) {
u64 >>= 4;
r += 4;
}
if (u64 >= (U64_LITERAL(1)<<2)) {
u64 >>= 2;
r += 2;
}
if (u64 >= (U64_LITERAL(1)<<1)) {
u64 >>= 1;
r += 1;
}
return r;
}
/** Return the power of 2 closest to <b>u64</b>. */
uint64_t
round_to_power_of_2(uint64_t u64)
{
int lg2 = tor_log2(u64);
uint64_t low = U64_LITERAL(1) << lg2, high = U64_LITERAL(1) << (lg2+1);
if (high - u64 < u64 - low)
return high;
else
return low;
}
/* =====
* String manipulation
* ===== */
......
......@@ -142,6 +142,10 @@ extern int dmalloc_free(const char *file, const int line, void *pnt,
/** Macro: true if two values have different boolean values. */
#define bool_neq(a,b) (!(a)!=!(b))
/* Math functions */
int tor_log2(uint64_t u64) ATTR_CONST;
uint64_t round_to_power_of_2(uint64_t u64);
/* String manipulation */
/** Allowable characters in a hexadecimal string. */
......
......@@ -946,6 +946,26 @@ test_util(void)
tor_gettimeofday(&end);
/* We might've timewarped a little. */
test_assert(tv_udiff(&start, &end) >= -5000);
/* Test tor_log2(). */
test_eq(tor_log2(64), 6);
test_eq(tor_log2(65), 6);
test_eq(tor_log2(63), 5);
test_eq(tor_log2(1), 0);
test_eq(tor_log2(2), 1);
test_eq(tor_log2(3), 1);
test_eq(tor_log2(4), 2);
test_eq(tor_log2(5), 2);
test_eq(tor_log2(U64_LITERAL(40000000000000000)), 55);
test_eq(tor_log2(UINT64_MAX), 63);
/* Test round_to_power_of_2 */
test_eq(round_to_power_of_2(120), 128);
test_eq(round_to_power_of_2(128), 128);
test_eq(round_to_power_of_2(130), 128);
test_eq(round_to_power_of_2(U64_LITERAL(40000000000000000)),
U64_LITERAL(1)<<55);
test_eq(round_to_power_of_2(0), 2);
}
static void
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment