Speed up bitwriter_grow_ by growing exponentially

Growing up to the max allowed size took roughly 4000 reallocations,
which can be expensive. Now grow exponentially, which requires
about 30 reallocations up to max size.

src/libFLAC/bitwriter.c

@@ -89,8 +89,8 @@ typedef FLAC__uint64 FLAC__bwtemp;
  * next one.
  */
 static const uint32_t FLAC__BITWRITER_DEFAULT_CAPACITY = 32768u / sizeof(bwword); /* size in words */
-/* When growing, increment 4K at a time */
-static const uint32_t FLAC__BITWRITER_DEFAULT_INCREMENT = 4096u / sizeof(bwword); /* size in words */
+/* When growing, increment with 1/4th at a time */
+static const uint32_t FLAC__BITWRITER_DEFAULT_GROW_FRACTION = 2; /* means grow by >> 2 (1/4th) of current size */
 
 #define FLAC__WORDS_TO_BITS(words) ((words) * FLAC__BITS_PER_WORD)
 #define FLAC__TOTAL_BITS(bw) (FLAC__WORDS_TO_BITS((bw)->words) + (bw)->bits)
@@ -131,11 +131,11 @@ FLAC__bool bitwriter_grow_(FLAC__BitWriter *bw, uint32_t bits_to_add)
 		 * To prevent chrashing, give up */
 		return false;
 
-	/* round up capacity increase to the nearest FLAC__BITWRITER_DEFAULT_INCREMENT */
-	if((new_capacity - bw->capacity) % FLAC__BITWRITER_DEFAULT_INCREMENT)
-		new_capacity += FLAC__BITWRITER_DEFAULT_INCREMENT - ((new_capacity - bw->capacity) % FLAC__BITWRITER_DEFAULT_INCREMENT);
+	/* As reallocation can be quite expensive, grow exponentially */
+	if((new_capacity - bw->capacity) < (bw->capacity >> FLAC__BITWRITER_DEFAULT_GROW_FRACTION))
+		new_capacity = bw->capacity + (bw->capacity >> FLAC__BITWRITER_DEFAULT_GROW_FRACTION);
+
 	/* make sure we got everything right */
-	FLAC__ASSERT(0 == (new_capacity - bw->capacity) % FLAC__BITWRITER_DEFAULT_INCREMENT);
 	FLAC__ASSERT(new_capacity > bw->capacity);
 	FLAC__ASSERT(new_capacity >= bw->words + ((bw->bits + bits_to_add + FLAC__BITS_PER_WORD - 1) / FLAC__BITS_PER_WORD));