[FFmpeg-devel] [PATCH] avformat/mpegvideodec: use avpriv_find_start_code in mpegvideo_probe()

[Michael Niedermayer]

On Sun, Mar 15, 2015 at 04:46:22PM +0800, zhaoxiu.zeng wrote:
> From 60cdc9161881cdf86e428a0d6812785938ae6667 Mon Sep 17 00:00:00 2001
> From: Zeng Zhaoxiu <zhaoxiu.zeng at gmail.com>
> Date: Sun, 15 Mar 2015 11:56:53 +0800
> Subject: [PATCH 2/7] avformat/mpegvideodec: use avpriv_find_start_code in
>  mpegvideo_probe()
> 
> Signed-off-by: Zeng Zhaoxiu <zhaoxiu.zeng at gmail.com>
> ---
>  libavformat/mpegvideodec.c | 34 ++++++++++++++++------------------
>  1 file changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/libavformat/mpegvideodec.c b/libavformat/mpegvideodec.c
> index ade76d8..c2fa6c2 100644
> --- a/libavformat/mpegvideodec.c
> +++ b/libavformat/mpegvideodec.c
> @@ -24,6 +24,7 @@
>  #include "rawdec.h"
>  
>  #include "libavutil/intreadwrite.h"
> +#include "libavcodec/internal.h"
>  
>  #define SEQ_START_CODE          0x000001b3
>  #define GOP_START_CODE          0x000001b8
> @@ -37,33 +38,30 @@ static int mpegvideo_probe(AVProbeData *p)
>  {
>      uint32_t code= -1;
>      int pic=0, seq=0, slice=0, pspack=0, vpes=0, apes=0, res=0, sicle=0;
> -    int i, j;
> +    const uint8_t *ptr = p->buf, *end = ptr + p->buf_size;
>      uint32_t last = 0;
> +    int j;
>  
> -    for(i=0; i<p->buf_size; i++){
> -        code = (code<<8) + p->buf[i];
> +    while (ptr < end) {
> +        ptr = avpriv_find_start_code(ptr, end, &code);
>          if ((code & 0xffffff00) == 0x100) {
> -            switch(code){
> +            switch (code) {
>              case     SEQ_START_CODE:
> -                if (!(p->buf[i+1+3+1+2] & 0x20))
> +                if (!(ptr[3 + 1 + 2] & 0x20))
>                      break;
> -                j = i;
> -                if (p->buf[j+8] & 2)
> -                    j+= 64;
> -                if (j >= p->buf_size)
> +                j = -1 + (ptr[-1 + 8] & 2) * 32;
> +                if (ptr + j >= end)
>                      break;
> -                if (p->buf[j+8] & 1)
> -                    j+= 64;
> -                if (j >= p->buf_size)
> +                j += (ptr[j + 8] & 1) * 64;
> +                if (ptr + j >= end)
>                      break;
> -                if (AV_RB24(p->buf + j + 9) & 0xFFFFFE)
> +                if (AV_RB24(ptr + j + 9) & 0xFFFFFE)
>                      break;
>                  seq++;
> -            break;
> -            case PICTURE_START_CODE:   pic++; break;
> +                break;
> +            case PICTURE_START_CODE:    pic++; break;
>              case    PACK_START_CODE: pspack++; break;
> -            case              0x1b6:
> -                                        res++; break;
> +            case              0x1b6:    res++; break;
>              }
>              if (code >= SLICE_START_CODE && code <= 0x1af) {
>                  if (last >= SLICE_START_CODE && last <= 0x1af) {

cleaned up and applied

also please do not mix unrelated cosmetic changes in the code
see for example the diff with these cosmetics removed, which i applied
its much more readable: (this is important for being reviewable)

diff --git a/libavformat/mpegvideodec.c b/libavformat/mpegvideodec.c
index ade76d86..5ea5569 100644
--- a/libavformat/mpegvideodec.c
+++ b/libavformat/mpegvideodec.c
@@ -24,6 +24,7 @@
 #include "rawdec.h"

 #include "libavutil/intreadwrite.h"
+#include "libavcodec/internal.h"

 #define SEQ_START_CODE          0x000001b3
 #define GOP_START_CODE          0x000001b8
@@ -37,26 +38,27 @@ static int mpegvideo_probe(AVProbeData *p)
 {
     uint32_t code= -1;
     int pic=0, seq=0, slice=0, pspack=0, vpes=0, apes=0, res=0, sicle=0;
-    int i, j;
+    const uint8_t *ptr = p->buf, *end = ptr + p->buf_size;
     uint32_t last = 0;
+    int j;

-    for(i=0; i<p->buf_size; i++){
-        code = (code<<8) + p->buf[i];
+    while (ptr < end) {
+        ptr = avpriv_find_start_code(ptr, end, &code);
         if ((code & 0xffffff00) == 0x100) {
             switch(code){
             case     SEQ_START_CODE:
-                if (!(p->buf[i+1+3+1+2] & 0x20))
+                if (!(ptr[3 + 1 + 2] & 0x20))
                     break;
-                j = i;
-                if (p->buf[j+8] & 2)
+                j = -1;
+                if (ptr[j + 8] & 2)
                     j+= 64;
-                if (j >= p->buf_size)
+                if (ptr + j >= end)
                     break;
-                if (p->buf[j+8] & 1)
+                if (ptr[j + 8] & 1)
                     j+= 64;
-                if (j >= p->buf_size)
+                if (ptr + j >= end)
                     break;
-                if (AV_RB24(p->buf + j + 9) & 0xFFFFFE)
+                if (AV_RB24(ptr + j + 9) & 0xFFFFFE)
                     break;
                 seq++;
             break;


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

He who knows, does not speak. He who speaks, does not know. -- Lao Tsu
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