From 8a2acbffc86012de3523ecf91db2c4ea1b1c4ea2 Mon Sep 17 00:00:00 2001
From: Mark Adler <madler@alumni.caltech.edu>
Date: Fri, 9 Sep 2011 23:13:27 -0700
Subject: zlib 1.0-pre

---
 crc32.c | 60 +++++++++---------------------------------------------------
 1 file changed, 9 insertions(+), 51 deletions(-)

(limited to 'crc32.c')

diff --git a/crc32.c b/crc32.c
index 7d6aa02..4089255 100644
--- a/crc32.c
+++ b/crc32.c
@@ -1,5 +1,5 @@
 /* crc32.c -- compute the CRC-32 of a data stream
- * Copyright (C) 1995-1996 Mark Adler
+ * Copyright (C) 1995 Mark Adler
  * For conditions of distribution and use, see copyright notice in zlib.h 
  */
 
@@ -10,53 +10,23 @@
 #define local static
 
 #ifdef DYNAMIC_CRC_TABLE
-
+/* =========================================================================
+ * Make the crc table. This function is needed only if you want to compute
+ * the table dynamically.
+ */
 local int crc_table_empty = 1;
-local uLongf crc_table[256];
-local void make_crc_table OF((void));
-
-/*
-  Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
-  x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
+local uLong crc_table[256];
 
-  Polynomials over GF(2) are represented in binary, one bit per coefficient,
-  with the lowest powers in the most significant bit.  Then adding polynomials
-  is just exclusive-or, and multiplying a polynomial by x is a right shift by
-  one.  If we call the above polynomial p, and represent a byte as the
-  polynomial q, also with the lowest power in the most significant bit (so the
-  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
-  where a mod b means the remainder after dividing a by b.
-
-  This calculation is done using the shift-register method of multiplying and
-  taking the remainder.  The register is initialized to zero, and for each
-  incoming bit, x^32 is added mod p to the register if the bit is a one (where
-  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
-  x (which is shifting right by one and adding x^32 mod p if the bit shifted
-  out is a one).  We start with the highest power (least significant bit) of
-  q and repeat for all eight bits of q.
-
-  The table is simply the CRC of all possible eight bit values.  This is all
-  the information needed to generate CRC's on data a byte at a time for all
-  combinations of CRC register values and incoming bytes.
-*/
 local void make_crc_table()
 {
   uLong c;
   int n, k;
-  uLong poly;            /* polynomial exclusive-or pattern */
-  /* terms of polynomial defining this crc (except x^32): */
-  static Byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
-
-  /* make exclusive-or pattern from polynomial (0xedb88320L) */
-  poly = 0L;
-  for (n = 0; n < sizeof(p)/sizeof(Byte); n++)
-    poly |= 1L << (31 - p[n]);
  
   for (n = 0; n < 256; n++)
   {
     c = (uLong)n;
     for (k = 0; k < 8; k++)
-      c = c & 1 ? poly ^ (c >> 1) : c >> 1;
+      c = c & 1 ? 0xedb88320L ^ (c >> 1) : c >> 1;
     crc_table[n] = c;
   }
   crc_table_empty = 0;
@@ -65,7 +35,7 @@ local void make_crc_table()
 /* ========================================================================
  * Table of CRC-32's of all single-byte values (made by make_crc_table)
  */
-local uLongf crc_table[256] = {
+local uLong crc_table[] = {
   0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
   0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
   0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
@@ -121,18 +91,6 @@ local uLongf crc_table[256] = {
 };
 #endif
 
-/* =========================================================================
- * This function can be used by asm versions of crc32()
- */
-uLongf *get_crc_table()
-{
-#ifdef DYNAMIC_CRC_TABLE
-  if (crc_table_empty) make_crc_table();
-#endif
-  return (uLongf *)crc_table;
-}
-
-/* ========================================================================= */
 #define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
 #define DO2(buf)  DO1(buf); DO1(buf);
 #define DO4(buf)  DO2(buf); DO2(buf);
@@ -141,7 +99,7 @@ uLongf *get_crc_table()
 /* ========================================================================= */
 uLong crc32(crc, buf, len)
     uLong crc;
-    const Bytef *buf;
+    Bytef *buf;
     uInt len;
 {
     if (buf == Z_NULL) return 0L;
-- 
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