[FFmpeg-devel] [PATCHv2] lavc/audiodsp: fix aliasing violation

* [FFmpeg-devel] [PATCHv2] lavc/audiodsp: fix aliasing violation
@ 2022-09-13 16:10 remi
  2022-09-17 18:39 ` Rémi Denis-Courmont
  0 siblings, 1 reply; 2+ messages in thread
From: remi @ 2022-09-13 16:10 UTC (permalink / raw)
  To: ffmpeg-devel

From: Rémi Denis-Courmont <remi@remlab.net>

Even though they have the same size, and typically the same alignment,
uint32_t and float are under no circumstances compatible types in C.

The casts from float * to uint32_t * are invalid here. Insofar as the
resulting pointers are dereferenced, this is undefined behaviour.
This patch uses av_float2int() / av_int2float() instead.
---
 libavcodec/audiodsp.c | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/libavcodec/audiodsp.c b/libavcodec/audiodsp.c
index ff43e87dce..8c0847f53f 100644
--- a/libavcodec/audiodsp.c
+++ b/libavcodec/audiodsp.c
@@ -22,36 +22,36 @@
 #include "libavutil/common.h"
 #include "audiodsp.h"
 
-static inline uint32_t clipf_c_one(uint32_t a, uint32_t mini,
-                                   uint32_t maxi, uint32_t maxisign)
+static inline float clipf_c_one(float a, uint32_t mini,
+                                uint32_t maxi, uint32_t maxisign)
 {
-    if (a > mini)
-        return mini;
-    else if ((a ^ (1U << 31)) > maxisign)
-        return maxi;
+    uint32_t ai = av_float2int(a);
+
+    if (ai > mini)
+        return av_int2float(mini);
+    else if ((ai ^ (1U << 31)) > maxisign)
+        return av_int2float(maxi);
     else
         return a;
 }
 
 static void vector_clipf_c_opposite_sign(float *dst, const float *src,
-                                         float *min, float *max, int len)
+                                         float min, float max, int len)
 {
     int i;
-    uint32_t mini        = *(uint32_t *) min;
-    uint32_t maxi        = *(uint32_t *) max;
+    uint32_t mini        = av_float2int(min);
+    uint32_t maxi        = av_float2int(max);
     uint32_t maxisign    = maxi ^ (1U << 31);
-    uint32_t *dsti       = (uint32_t *) dst;
-    const uint32_t *srci = (const uint32_t *) src;
 
     for (i = 0; i < len; i += 8) {
-        dsti[i + 0] = clipf_c_one(srci[i + 0], mini, maxi, maxisign);
-        dsti[i + 1] = clipf_c_one(srci[i + 1], mini, maxi, maxisign);
-        dsti[i + 2] = clipf_c_one(srci[i + 2], mini, maxi, maxisign);
-        dsti[i + 3] = clipf_c_one(srci[i + 3], mini, maxi, maxisign);
-        dsti[i + 4] = clipf_c_one(srci[i + 4], mini, maxi, maxisign);
-        dsti[i + 5] = clipf_c_one(srci[i + 5], mini, maxi, maxisign);
-        dsti[i + 6] = clipf_c_one(srci[i + 6], mini, maxi, maxisign);
-        dsti[i + 7] = clipf_c_one(srci[i + 7], mini, maxi, maxisign);
+        dst[i + 0] = clipf_c_one(src[i + 0], mini, maxi, maxisign);
+        dst[i + 1] = clipf_c_one(src[i + 1], mini, maxi, maxisign);
+        dst[i + 2] = clipf_c_one(src[i + 2], mini, maxi, maxisign);
+        dst[i + 3] = clipf_c_one(src[i + 3], mini, maxi, maxisign);
+        dst[i + 4] = clipf_c_one(src[i + 4], mini, maxi, maxisign);
+        dst[i + 5] = clipf_c_one(src[i + 5], mini, maxi, maxisign);
+        dst[i + 6] = clipf_c_one(src[i + 6], mini, maxi, maxisign);
+        dst[i + 7] = clipf_c_one(src[i + 7], mini, maxi, maxisign);
     }
 }
 
@@ -61,7 +61,7 @@ static void vector_clipf_c(float *dst, const float *src, int len,
     int i;
 
     if (min < 0 && max > 0) {
-        vector_clipf_c_opposite_sign(dst, src, &min, &max, len);
+        vector_clipf_c_opposite_sign(dst, src, min, max, len);
     } else {
         for (i = 0; i < len; i += 8) {
             dst[i]     = av_clipf(src[i], min, max);
-- 
2.37.2

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