Fix deflateBound and compressBound returning very small size estimates.

Remove workaround in switchlevels.c, so we do actual testing of this.
Use named defines instead of magic numbers where we can.

diff --git a/compress.c b/compress.c
index de45e29e6a2aaea214cd9f8b8c6d926d167341a9..fded2a4cdf65b37cd1d76e050c94a1c239da8f0e 100644 (file)
--- a/compress.c
+++ b/compress.c
@@ -91,10 +91,11 @@ 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 & gzip headers and footers */
-    return sourceLen + ((sourceLen + 13 + 7) >> 3) + 18;
+    return sourceLen                       /* The source size itself */
+      + DEFLATE_QUICK_OVERHEAD(sourceLen)  /* Source encoding overhead, padded to next full byte */
+      + DEFLATE_BLOCK_OVERHEAD             /* Deflate block overhead bytes */
+      + ZLIB_WRAPLEN;                      /* zlib wrapper */
 #else
-    return sourceLen + (sourceLen >> 12) + (sourceLen >> 14) + (sourceLen >> 25) + 13;
+    return sourceLen + (sourceLen >> 4) + 7 + ZLIB_WRAPLEN;
 #endif
 }

diff --git a/deflate.c b/deflate.c
index bb20a7d7a683f4cfcf326a65c38330b00d33c165..8f569bf2e57bba2bbb9c271df1eefd0b3ebb51f3 100644 (file)
--- a/deflate.c
+++ b/deflate.c
@@ -611,11 +611,11 @@ unsigned long Z_EXPORT PREFIX(deflateBound)(PREFIX3(stream) *strm, unsigned long
         wraplen = 0;
         break;
     case 1:                                 /* zlib wrapper */
-        wraplen = 6 + (s->strstart ? 4 : 0);
+        wraplen = ZLIB_WRAPLEN + (s->strstart ? 4 : 0);
         break;
 #ifdef GZIP
     case 2:                                 /* gzip wrapper */
-        wraplen = 18;
+        wraplen = GZIP_WRAPLEN;
         if (s->gzhead != NULL) {            /* user-supplied gzip header */
             unsigned char *str;
             if (s->gzhead->extra != NULL) {
@@ -639,7 +639,7 @@ unsigned long Z_EXPORT PREFIX(deflateBound)(PREFIX3(stream) *strm, unsigned long
         break;
 #endif
     default:                                /* for compiler happiness */
-        wraplen = 6;
+        wraplen = ZLIB_WRAPLEN;
     }
 
     /* if not default parameters, return conservative bound */
@@ -647,8 +647,14 @@ unsigned long Z_EXPORT PREFIX(deflateBound)(PREFIX3(stream) *strm, unsigned long
             s->w_bits != 15 || HASH_BITS < 15)
         return complen + wraplen;
 
-    /* default settings: return tight bound for that case */
-    return sourceLen + (sourceLen >> 12) + (sourceLen >> 14) + (sourceLen >> 25) + 13 - 6 + wraplen;
+#ifndef NO_QUICK_STRATEGY
+    return sourceLen                       /* The source size itself */
+      + DEFLATE_QUICK_OVERHEAD(sourceLen)  /* Source encoding overhead, padded to next full byte */
+      + DEFLATE_BLOCK_OVERHEAD             /* Deflate block overhead bytes */
+      + wraplen;                           /* none, zlib or gzip wrapper */
+#else
+    return sourceLen + (sourceLen >> 4) + 7 + wraplen;
+#endif
 }
 
 /* =========================================================================

diff --git a/test/switchlevels.c b/test/switchlevels.c
index a4ec4b7c76c8d2f3bc1970797edf954f8959acdd..1e1fb00a5cffa950f1a80a572f5c6ae2fbcbee13 100644 (file)
--- a/test/switchlevels.c
+++ b/test/switchlevels.c
@@ -68,7 +68,7 @@ static int compress_chunk(PREFIX3(stream) *strm, int level, int size, int last)
         goto done;
     }
 
-    compsize = 100 + 2 * PREFIX(deflateBound)(strm, size);
+    compsize = PREFIX(deflateBound)(strm, size);
     buf = malloc(size + compsize);
     if (buf == NULL) {
         fprintf(stderr, "Out of memory\n");

diff --git a/zutil.h b/zutil.h
index e7cb9ad3e470744f9607c4fdf19236bd723865a1..f25556f946cd9a4cbbea0d214cc16891cf499f14 100644 (file)
--- a/zutil.h
+++ b/zutil.h
@@ -78,7 +78,19 @@ 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 ZLIB_WRAPLEN 6      /* zlib format overhead */
+#define GZIP_WRAPLEN 18     /* gzip format overhead */
+
+#define DEFLATE_HEADER_BITS 3
+#define DEFLATE_EOBS_BITS   15
+#define DEFLATE_PAD_BITS    6
+#define DEFLATE_BLOCK_OVERHEAD ((DEFLATE_HEADER_BITS + DEFLATE_EOBS_BITS + DEFLATE_PAD_BITS) >> 3)
+/* deflate block overhead: 3 bits for block start + 15 bits for block end + padding to nearest byte */
+
+#define DEFLATE_QUICK_LIT_MAX_BITS 9
+#define DEFLATE_QUICK_OVERHEAD(x) ((x * (DEFLATE_QUICK_LIT_MAX_BITS - 8) + 7) >> 3)
+/* deflate_quick worst-case overhead: 9 bits per literal, round up to next byte (+7) */
+
 
         /* target dependencies */