On Thu, Apr 28, 2011 at 5:08 AM, Måns Rullgård <[email protected]> wrote:
> Aℓex Converse <[email protected]> writes:
>
>> From ae62aa2fca3b2cf45a98dc2f9777065bcb452797 Mon Sep 17 00:00:00 2001
>> From: Alex Converse <[email protected]>
>> Date: Tue, 26 Apr 2011 09:08:26 -0700
>> Subject: [PATCH 3/4] bitstream: Properly promote av_reverse values before
>> shifting.
>> MIME-Version: 1.0
>> Content-Type: multipart/mixed; boundary="------------1"
>>
>> This is a multi-part message in MIME format.
>> --------------1
>> Content-Type: text/plain; charset=UTF-8; format=fixed
>> Content-Transfer-Encoding: 8bit
>>
>> ---
>> libavcodec/bitstream.c | 8 ++++----
>> 1 files changed, 4 insertions(+), 4 deletions(-)
>>
>> --------------1
>> Content-Type: text/x-patch;
>> name="0003-bitstream-Properly-promote-av_reverse-values-before-.patch"
>> Content-Transfer-Encoding: 8bit
>> Content-Disposition: attachment;
>> filename="0003-bitstream-Properly-promote-av_reverse-values-before-.patch"
>>
>> diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c
>> index 329ec95..14c3eaa 100644
>> --- a/libavcodec/bitstream.c
>> +++ b/libavcodec/bitstream.c
>> @@ -118,10 +118,10 @@ static int alloc_table(VLC *vlc, int size, int
>> use_static)
>> }
>>
>> static av_always_inline uint32_t bitswap_32(uint32_t x) {
>> - return av_reverse[x&0xFF]<<24
>> - | av_reverse[(x>>8)&0xFF]<<16
>> - | av_reverse[(x>>16)&0xFF]<<8
>> - | av_reverse[x>>24];
>> + return (uint32_t)av_reverse[x&0xFF]<<24
>> + | (uint32_t)av_reverse[(x>>8)&0xFF]<<16
>> + | (uint32_t)av_reverse[(x>>16)&0xFF]<<8
>> + | (uint32_t)av_reverse[x>>24];
>> }
>
> The integer promotions already do this.
>
We are operating on uint8_t and int. The promoted the result is an int
because the full range of uint8_t can fit in int.
Consider the following program:
#include <stdio.h>
#include <stdint.h>
static const uint8_t arr[] = { 128, 129, 130};
int main() {
int x;
typeof(x) y;
printf(" int32_t %d\n",
__builtin_types_compatible_p(typeof(arr[1]<<24), int32_t));
printf("uint32_t %d\n",
__builtin_types_compatible_p(typeof(arr[1]<<24), uint32_t));
return 0;
}
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