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liblzma: Use lzma_alloc_zero() in LZ encoder initialization.

Browse source 
This avoids a memzero() call for a newly-allocated memory,
which can be expensive when encoding small streams with
an over-sized dictionary.

To avoid using lzma_alloc_zero() for memory that doesn't
need to be zeroed, lzma_mf.son is now allocated separately,
which requires handling it separately in normalize() too.

Thanks to Vincenzo Innocente for reporting the problem.
This commit is contained in:
Lasse Collin 2014-05-25 21:45:56 +03:00
parent 28af24e9cf
commit da1718f266
3 changed files with 64 additions and 57 deletions
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86
src/liblzma/lz/lz_encoder.c
View file

@ -326,25 +326,22 @@ lz_encoder_prepare(lzma_mf *mf, const lzma_allocator *allocator,
hs += HASH_4_SIZE;
*/
// If the above code calculating hs is modified, make sure that
// this assertion stays valid (UINT32_MAX / 5 is not strictly the
// exact limit). If it doesn't, you need to calculate that
// hash_size_sum + sons_count cannot overflow.
assert(hs < UINT32_MAX / 5);
const uint32_t old_count = mf->hash_size_sum + mf->sons_count;
mf->hash_size_sum = hs;
const uint32_t old_hash_count = mf->hash_count;
const uint32_t old_sons_count = mf->sons_count;
mf->hash_count = hs;
mf->sons_count = mf->cyclic_size;
if (is_bt)
mf->sons_count *= 2;
const uint32_t new_count = mf->hash_size_sum + mf->sons_count;
// Deallocate the old hash array if it exists and has different size
// than what is needed now.
if (old_count != new_count) {
if (old_hash_count != mf->hash_count
|| old_sons_count != mf->sons_count) {
lzma_free(mf->hash, allocator);
mf->hash = NULL;
lzma_free(mf->son, allocator);
mf->son = NULL;
}
// Maximum number of match finder cycles
@ -382,44 +379,49 @@ lz_encoder_init(lzma_mf *mf, const lzma_allocator *allocator,
mf->write_pos = 0;
mf->pending = 0;
// Allocate match finder's hash array.
const size_t alloc_count = mf->hash_size_sum + mf->sons_count;
#if UINT32_MAX >= SIZE_MAX / 4
// Check for integer overflow. (Huge dictionaries are not
// possible on 32-bit CPU.)
if (alloc_count > SIZE_MAX / sizeof(uint32_t))
if (mf->hash_count > SIZE_MAX / sizeof(uint32_t)
|| mf->sons_count > SIZE_MAX / sizeof(uint32_t))
return true;
#endif
// Allocate and initialize the hash table. Since EMPTY_HASH_VALUE
// is zero, we can use lzma_alloc_zero() or memzero() for mf->hash.
//
// We don't need to initialize mf->son, but not doing that may
// make Valgrind complain in normalization (see normalize() in
// lz_encoder_mf.c). Skipping the initialization is *very* good
// when big dictionary is used but only small amount of data gets
// actually compressed: most of the mf->son won't get actually
// allocated by the kernel, so we avoid wasting RAM and improve
// initialization speed a lot.
if (mf->hash == NULL) {
mf->hash = lzma_alloc(alloc_count * sizeof(uint32_t),
mf->hash = lzma_alloc_zero(mf->hash_count * sizeof(uint32_t),
allocator);
if (mf->hash == NULL)
mf->son = lzma_alloc(mf->sons_count * sizeof(uint32_t),
allocator);
if (mf->hash == NULL || mf->son == NULL) {
lzma_free(mf->hash, allocator);
mf->hash = NULL;
lzma_free(mf->son, allocator);
mf->son = NULL;
return true;
}
} else {
/*
for (uint32_t i = 0; i < mf->hash_count; ++i)
mf->hash[i] = EMPTY_HASH_VALUE;
*/
memzero(mf->hash, mf->hash_count * sizeof(uint32_t));
}
mf->son = mf->hash + mf->hash_size_sum;
mf->cyclic_pos = 0;
// Initialize the hash table. Since EMPTY_HASH_VALUE is zero, we
// can use memset().
/*
for (uint32_t i = 0; i < hash_size_sum; ++i)
mf->hash[i] = EMPTY_HASH_VALUE;
*/
memzero(mf->hash, (size_t)(mf->hash_size_sum) * sizeof(uint32_t));
// We don't need to initialize mf->son, but not doing that will
// make Valgrind complain in normalization (see normalize() in
// lz_encoder_mf.c).
//
// Skipping this initialization is *very* good when big dictionary is
// used but only small amount of data gets actually compressed: most
// of the mf->hash won't get actually allocated by the kernel, so
// we avoid wasting RAM and improve initialization speed a lot.
//memzero(mf->son, (size_t)(mf->sons_count) * sizeof(uint32_t));
// Handle preset dictionary.
if (lz_options->preset_dict != NULL
&& lz_options->preset_dict_size > 0) {
@ -446,7 +448,8 @@ lzma_lz_encoder_memusage(const lzma_lz_options *lz_options)
lzma_mf mf = {
.buffer = NULL,
.hash = NULL,
.hash_size_sum = 0,
.son = NULL,
.hash_count = 0,
.sons_count = 0,
};
@ -455,9 +458,8 @@ lzma_lz_encoder_memusage(const lzma_lz_options *lz_options)
return UINT64_MAX;
// Calculate the memory usage.
return (uint64_t)(mf.hash_size_sum + mf.sons_count)
* sizeof(uint32_t)
+ (uint64_t)(mf.size) + sizeof(lzma_coder);
return ((uint64_t)(mf.hash_count) + mf.sons_count) * sizeof(uint32_t)
+ mf.size + sizeof(lzma_coder);
}
@ -466,6 +468,7 @@ lz_encoder_end(lzma_coder *coder, const lzma_allocator *allocator)
{
lzma_next_end(&coder->next, allocator);
lzma_free(coder->mf.son, allocator);
lzma_free(coder->mf.hash, allocator);
lzma_free(coder->mf.buffer, allocator);
@ -523,7 +526,8 @@ lzma_lz_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
next->coder->mf.buffer = NULL;
next->coder->mf.hash = NULL;
next->coder->mf.hash_size_sum = 0;
next->coder->mf.son = NULL;
next->coder->mf.hash_count = 0;
next->coder->mf.sons_count = 0;
next->coder->next = LZMA_NEXT_CODER_INIT;

2
src/liblzma/lz/lz_encoder.h
View file

@ -119,7 +119,7 @@ struct lzma_mf_s {
lzma_action action;
/// Number of elements in hash[]
uint32_t hash_size_sum;
uint32_t hash_count;
/// Number of elements in son[]
uint32_t sons_count;

33
src/liblzma/lz/lz_encoder_mf.c
View file

@ -116,24 +116,27 @@ normalize(lzma_mf *mf)
= (MUST_NORMALIZE_POS - mf->cyclic_size);
// & (~(UINT32_C(1) << 10) - 1);
const uint32_t count = mf->hash_size_sum + mf->sons_count;
uint32_t *hash = mf->hash;
for (uint32_t i = 0; i < count; ++i) {
for (uint32_t i = 0; i < mf->hash_count; ++i) {
// If the distance is greater than the dictionary size,
// we can simply mark the hash element as empty.
//
// NOTE: Only the first mf->hash_size_sum elements are
// initialized for sure. There may be uninitialized elements
// in mf->son. Since we go through both mf->hash and
// mf->son here in normalization, Valgrind may complain
// that the "if" below depends on uninitialized value. In
// this case it is safe to ignore the warning. See also the
// comments in lz_encoder_init() in lz_encoder.c.
if (hash[i] <= subvalue)
hash[i] = EMPTY_HASH_VALUE;
if (mf->hash[i] <= subvalue)
mf->hash[i] = EMPTY_HASH_VALUE;
else
hash[i] -= subvalue;
mf->hash[i] -= subvalue;
}
for (uint32_t i = 0; i < mf->sons_count; ++i) {
// Do the same for mf->son.
//
// NOTE: There may be uninitialized elements in mf->son.
// Valgrind may complain that the "if" below depends on
// an uninitialized value. In this case it is safe to ignore
// the warning. See also the comments in lz_encoder_init()
// in lz_encoder.c.
if (mf->son[i] <= subvalue)
mf->son[i] = EMPTY_HASH_VALUE;
else
mf->son[i] -= subvalue;
}
// Update offset to match the new locations.