Messages in this thread Patch in this message | | | From | Lasse Collin <> | Subject | [PATCH 07/11] xz: Optimize for-loop conditions in the BCJ decoders | Date | Wed, 20 Mar 2024 20:38:40 +0200 |
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Compilers cannot optimize the addition "i + 4" away since theoretically it could overflow.
Reviewed-by: Jia Tan <jiat0218@gmail.com> Signed-off-by: Lasse Collin <lasse.collin@tukaani.org> --- lib/xz/xz_dec_bcj.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/lib/xz/xz_dec_bcj.c b/lib/xz/xz_dec_bcj.c index ab9237ed6db8..e0b4bf4999c0 100644 --- a/lib/xz/xz_dec_bcj.c +++ b/lib/xz/xz_dec_bcj.c @@ -161,7 +161,9 @@ static size_t bcj_powerpc(struct xz_dec_bcj *s, uint8_t *buf, size_t size) size_t i; uint32_t instr; - for (i = 0; i + 4 <= size; i += 4) { + size &= ~(size_t)3; + + for (i = 0; i < size; i += 4) { instr = get_unaligned_be32(buf + i); if ((instr & 0xFC000003) == 0x48000001) { instr &= 0x03FFFFFC; @@ -218,7 +220,9 @@ static size_t bcj_ia64(struct xz_dec_bcj *s, uint8_t *buf, size_t size) /* Instruction normalized with bit_res for easier manipulation */ uint64_t norm; - for (i = 0; i + 16 <= size; i += 16) { + size &= ~(size_t)15; + + for (i = 0; i < size; i += 16) { mask = branch_table[buf[i] & 0x1F]; for (slot = 0, bit_pos = 5; slot < 3; ++slot, bit_pos += 41) { if (((mask >> slot) & 1) == 0) @@ -266,7 +270,9 @@ static size_t bcj_arm(struct xz_dec_bcj *s, uint8_t *buf, size_t size) size_t i; uint32_t addr; - for (i = 0; i + 4 <= size; i += 4) { + size &= ~(size_t)3; + + for (i = 0; i < size; i += 4) { if (buf[i + 3] == 0xEB) { addr = (uint32_t)buf[i] | ((uint32_t)buf[i + 1] << 8) | ((uint32_t)buf[i + 2] << 16); @@ -289,7 +295,12 @@ static size_t bcj_armthumb(struct xz_dec_bcj *s, uint8_t *buf, size_t size) size_t i; uint32_t addr; - for (i = 0; i + 4 <= size; i += 2) { + if (size < 4) + return 0; + + size -= 4; + + for (i = 0; i <= size; i += 2) { if ((buf[i + 1] & 0xF8) == 0xF0 && (buf[i + 3] & 0xF8) == 0xF8) { addr = (((uint32_t)buf[i + 1] & 0x07) << 19) @@ -317,7 +328,9 @@ static size_t bcj_sparc(struct xz_dec_bcj *s, uint8_t *buf, size_t size) size_t i; uint32_t instr; - for (i = 0; i + 4 <= size; i += 4) { + size &= ~(size_t)3; + + for (i = 0; i < size; i += 4) { instr = get_unaligned_be32(buf + i); if ((instr >> 22) == 0x100 || (instr >> 22) == 0x1FF) { instr <<= 2; -- 2.44.0
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