Add crc32_combine_gen() and crc32_combine_op() for fast combines.

When the same len2 is used repeatedly, it is faster to use
crc32_combine_gen() to generate an operator, that is then used to
combine CRCs with crc32_combine_op().

1 files changed, 22 insertions, 0 deletions

diff --git a/zlib.h b/zlib.h
index 0b74b25..14d87a2 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1757,6 +1757,22 @@ ZEXTERN uLong ZEXPORT crc32_combine OF((uLong crc1, uLong crc2, z_off_t len2));
    len2.
 */
 
+/*
+ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t op[32], z_off_t len2));
+
+     Generate the operator op corresponding to length len2, to be used with
+   crc32_combine_op(). op must have room for 32 z_crc_t values. (32 is the
+   number of bits in the CRC.)
+*/
+
+ZEXTERN uLong ZEXPORT crc32_combine_op OF((uLong crc1, uLong crc2,
+                                           const z_crc_t *op));
+/*
+     Give the same result as crc32_combine(), using op in place of len2. op is
+   is generated from len2 by crc32_combine_gen(). This will be faster than
+   crc32_combine() if the generated op is used many times.
+*/
+
 
                         /* various hacks, don't look :) */
 
@@ -1844,6 +1860,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file));  /* backward compatibility */
    ZEXTERN z_off64_t ZEXPORT gzoffset64 OF((gzFile));
    ZEXTERN uLong ZEXPORT adler32_combine64 OF((uLong, uLong, z_off64_t));
    ZEXTERN uLong ZEXPORT crc32_combine64 OF((uLong, uLong, z_off64_t));
+   ZEXTERN void ZEXPORT crc32_combine_gen64 OF((z_crc_t *op, z_off64_t));
 #endif
 
 #if !defined(ZLIB_INTERNAL) && defined(Z_WANT64)
@@ -1854,6 +1871,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file));  /* backward compatibility */
 #    define z_gzoffset z_gzoffset64
 #    define z_adler32_combine z_adler32_combine64
 #    define z_crc32_combine z_crc32_combine64
+#    define z_crc32_combine_gen z_crc32_combine64_gen
 #  else
 #    define gzopen gzopen64
 #    define gzseek gzseek64
@@ -1861,6 +1879,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file));  /* backward compatibility */
 #    define gzoffset gzoffset64
 #    define adler32_combine adler32_combine64
 #    define crc32_combine crc32_combine64
+#    define crc32_combine_gen crc32_combine_gen64
 #  endif
 #  ifndef Z_LARGE64
      ZEXTERN gzFile ZEXPORT gzopen64 OF((const char *, const char *));
@@ -1869,6 +1888,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file));  /* backward compatibility */
      ZEXTERN z_off_t ZEXPORT gzoffset64 OF((gzFile));
      ZEXTERN uLong ZEXPORT adler32_combine64 OF((uLong, uLong, z_off_t));
      ZEXTERN uLong ZEXPORT crc32_combine64 OF((uLong, uLong, z_off_t));
+     ZEXTERN void ZEXPORT crc32_combine_gen64 OF((z_crc_t *op, z_off_t));
 #  endif
 #else
    ZEXTERN gzFile ZEXPORT gzopen OF((const char *, const char *));
@@ -1877,12 +1897,14 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file));  /* backward compatibility */
    ZEXTERN z_off_t ZEXPORT gzoffset OF((gzFile));
    ZEXTERN uLong ZEXPORT adler32_combine OF((uLong, uLong, z_off_t));
    ZEXTERN uLong ZEXPORT crc32_combine OF((uLong, uLong, z_off_t));
+   ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t *op, z_off_t));
 #endif
 
 #else /* Z_SOLO */
 
    ZEXTERN uLong ZEXPORT adler32_combine OF((uLong, uLong, z_off_t));
    ZEXTERN uLong ZEXPORT crc32_combine OF((uLong, uLong, z_off_t));
+   ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t *op, z_off_t));
 
 #endif /* !Z_SOLO */