dr_mp3: Fix an error when padding is malformed.

Author: mackron

dr_mp3.h

@@ -3202,8 +3202,17 @@ static drmp3_bool32 drmp3_init_internal(drmp3* pMP3, drmp3_read_proc onRead, drm
                         pTagData += 21;
 
                         if (pTagData - pFirstFrameData + 14 < firstFrameInfo.frame_bytes) {
-                            pMP3->delayInPCMFrames   = (( (drmp3_uint32)pTagData[0]        << 4) | ((drmp3_uint32)pTagData[1] >> 4)) + (528 + 1);
-                            pMP3->paddingInPCMFrames = ((((drmp3_uint32)pTagData[1] & 0xF) << 8) | ((drmp3_uint32)pTagData[2]     )) - (528 + 1);
+                            int delayInPCMFrames;
+                            int paddingInPCMFrames;
+
+                            delayInPCMFrames   = (( (drmp3_uint32)pTagData[0]        << 4) | ((drmp3_uint32)pTagData[1] >> 4)) + (528 + 1);
+                            paddingInPCMFrames = ((((drmp3_uint32)pTagData[1] & 0xF) << 8) | ((drmp3_uint32)pTagData[2]     )) - (528 + 1);
+                            if (paddingInPCMFrames < 0) {
+                                paddingInPCMFrames = 0; /* Padding cannot be negative. Probably a malformed file. Ignore. */
+                            }
+                            
+                            pMP3->delayInPCMFrames   = (drmp3_uint32)delayInPCMFrames;
+                            pMP3->paddingInPCMFrames = (drmp3_uint32)paddingInPCMFrames;
                         }
                     }
 
@@ -4515,15 +4524,30 @@ DRMP3_API drmp3_bool32 drmp3_get_mp3_and_pcm_frame_count(drmp3* pMP3, drmp3_uint
 
 DRMP3_API drmp3_uint64 drmp3_get_pcm_frame_count(drmp3* pMP3)
 {
+    drmp3_uint64 totalPCMFrameCount;
+
     if (pMP3 == NULL) {
         return 0;
     }
 
     if (pMP3->totalPCMFrameCount != DRMP3_UINT64_MAX) {
-        return (drmp3_uint64)pMP3->totalPCMFrameCount - pMP3->paddingInPCMFrames - pMP3->delayInPCMFrames;
+        totalPCMFrameCount = pMP3->totalPCMFrameCount;
+
+        if (totalPCMFrameCount >= pMP3->delayInPCMFrames) {
+            totalPCMFrameCount -= pMP3->delayInPCMFrames;
+        } else {
+            /* The delay is greater than the frame count reported by the Xing/Info tag. Assume it's invalid and ignore. */
+        }
+
+        if (totalPCMFrameCount >= pMP3->paddingInPCMFrames) {
+            totalPCMFrameCount -= pMP3->paddingInPCMFrames;
+        } else {
+            /* The padding is greater than the frame count reported by the Xing/Info tag. Assume it's invalid and ignore. */
+        }
+
+        return totalPCMFrameCount;
     } else {
         /* Unknown frame count. Need to calculate it. */
-        drmp3_uint64 totalPCMFrameCount;
         if (!drmp3_get_mp3_and_pcm_frame_count(pMP3, NULL, &totalPCMFrameCount)) {
             return 0;
         }