Bug 1412942 - pad Mac font data when checksumming. r=jfkthame

MozReview-Commit-ID: 3941eAWNXoR

gfx/2d/ScaledFontMac.cpp

@@ -175,7 +175,7 @@ CalcTableChecksum(const uint32_t *tableStart, uint32_t length, bool skipChecksum
 {
     uint32_t sum = 0L;
     const uint32_t *table = tableStart;
-    const uint32_t *end = table+((length+3) & ~3) / sizeof(uint32_t);
+    const uint32_t *end = table + length / sizeof(uint32_t);
     while (table < end) {
         if (skipChecksumAdjust && (table - tableStart) == 2) {
             table++;
@@ -183,6 +183,15 @@ CalcTableChecksum(const uint32_t *tableStart, uint32_t length, bool skipChecksum
             sum += CFSwapInt32BigToHost(*table++);
         }
     }
+
+    // The length is not 4-byte aligned, but we still must process the remaining bytes.
+    if (length & 3) {
+        // Pad with zero before adding to the checksum.
+        uint32_t last = 0;
+        memcpy(&last, end, length & 3);
+        sum += CFSwapInt32BigToHost(last);
+    }
+
     return sum;
 }