Use named define instead of magic number for deflate block header ove…

…rhead and padding.
zlib-ng · Dec 14, 2021 · 855c712 · 855c712
1 parent 4134223
commit 855c712
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Showing 3 changed files with 10 additions and 10 deletions.
diff --git a/compress.c b/compress.c
@@ -91,10 +91,9 @@ z_size_t Z_EXPORT PREFIX(compressBound)(z_size_t sourceLen) {
         return complen + ZLIB_WRAPLEN;
 
 #ifndef NO_QUICK_STRATEGY
-    /* Quick deflate strategy worse case is 9 bits per literal, rounded to nearest byte,
-       plus the size of block & zlib headers and footers, and one extra byte for padding
-       extremely small blocks */
-    return sourceLen + ((sourceLen + 13 + 7) >> 3) + ZLIB_WRAPLEN + 1;
+    /* Quick deflate strategy worst case is 9 bits per literal, rounded to nearest byte (+7 bits),
+       plus the size of deflate block headers, padding and zlib wrapper */
+    return sourceLen + ((sourceLen + 7) >> 3) + ((DEFLATE_WRAPBITS + DEFLATE_PADBITS) >> 3) + ZLIB_WRAPLEN;
 #else
     return sourceLen + (sourceLen >> 4) + 7 + ZLIB_WRAPLEN;
 #endif

diff --git a/deflate.c b/deflate.c
@@ -648,10 +648,9 @@ unsigned long Z_EXPORT PREFIX(deflateBound)(PREFIX3(stream) *strm, unsigned long
         return complen + wraplen;
 
 #ifndef NO_QUICK_STRATEGY
-    /* Quick deflate strategy worst case is 9 bits per literal, rounded to nearest byte,
-       plus the size of block headers & wrappers, and one extra byte for padding
-       extremely small blocks */
-    return sourceLen + ((sourceLen + 13 + 7) >> 3) + wraplen + 1;
+    /* Quick deflate strategy worst case is 9 bits per literal, rounded to nearest byte (+7 bits),
+       plus the size of deflate block headers, padding and zlib/gzip wrapper */
+    return sourceLen + ((sourceLen + 7) >> 3) + ((DEFLATE_WRAPBITS + DEFLATE_PADBITS) >> 3) + wraplen;
 #else
     return sourceLen + (sourceLen >> 4) + 7 + wraplen;
 #endif

diff --git a/zutil.h b/zutil.h
@@ -78,8 +78,10 @@ extern z_const char * const PREFIX(z_errmsg)[10]; /* indexed by 2-zlib_error */
 #define ADLER32_INITIAL_VALUE 1 /* initial adler-32 hash value */
 #define CRC32_INITIAL_VALUE   0 /* initial crc-32 hash value */
 
-#define ZLIB_WRAPLEN 6  /* zlib format overhead */
-#define GZIP_WRAPLEN 18 /* gzip format overhead */
+#define ZLIB_WRAPLEN 6      /* zlib format overhead */
+#define GZIP_WRAPLEN 18     /* gzip format overhead */
+#define DEFLATE_WRAPBITS 13 /* deflate block overhead: 3 bits for block start + 10 bits for block end */
+#define DEFLATE_PADBITS 3   /* padding used to round deflate_wrapbits up to nearest byte */
 
         /* target dependencies */