[svn-r12607] Description:

    Tweak the library's new faster fletcher32 algorithm to always produce the
same checksum as the previous fletcher32 code in the fletcher32 I/O pipeline
filter and switch the filter to use the library's version of the algorithm.

Tested on:
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)
    Too minor to require h5committest

3 files changed, 14 insertions, 74 deletions

diff --git a/src/H5Zfletcher32.c b/src/H5Zfletcher32.c
index 770d05a..9092452 100644
--- a/src/H5Zfletcher32.c
+++ b/src/H5Zfletcher32.c
@@ -48,71 +48,6 @@ const H5Z_class_t H5Z_FLETCHER32[1] = {{
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5Z_filter_fletcher32_compute
- *
- * Purpose:	Implement an Fletcher32 Checksum using 1's complement.
- *
- * Return:	Success: Fletcher32 value
- *
- *		Failure: Can't fail
- *
- * Programmer:	Raymond Lu
- *              Jan 3, 2003
- *
- * Modifications: Pedro Vicente, March 10, 2004
- *   defined *SRC as unsigned char for all cases
- *
- *-------------------------------------------------------------------------
- */
-static uint32_t
-H5Z_filter_fletcher32_compute(void *_src, size_t len)
-{
-    unsigned char *src=(unsigned char *)_src;
-    size_t count = len;         /* Number of bytes left to checksum */
-    uint32_t s1 = 0, s2 = 0;    /* Temporary partial checksums */
-
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5Z_filter_fletcher32_compute)
-
-    /* Compute checksum */
-    while(count > 1) {
-        unsigned short tmp_src;     /*To handle unusual platforms like Cray*/
-
-        tmp_src = (((unsigned short)src[0])<<8) | ((unsigned short)src[1]);
-        src +=2;
-        s1 += tmp_src;
-
-        if(s1 & 0xFFFF0000) { /*Wrap around carry if occurred*/
-            s1 &= 0xFFFF;
-            s1++;
-        }
-        s2 += s1;
-        if(s2 & 0xFFFF0000) { /*Wrap around carry if occurred*/
-            s2 &= 0xFFFF;
-            s2++;
-        }
-        count -= 2;
-    }
-
-    /* Check for single byte remaining */
-    if(count==1) {
-        s1 += *(unsigned char*)src;
-        if(s1 & 0xFFFF0000) { /*Wrap around carry if occurred*/
-            s1 &= 0xFFFF;
-            s1++;
-        }
-        s2 += s1;
-        if(s2 & 0xFFFF0000) { /*Wrap around carry if occurred*/
-            s2 &= 0xFFFF;
-            s2++;
-        }
-    }
-
-    FUNC_LEAVE_NOAPI((s2 << 16) + s1)
-}
-
-
-
-/*-------------------------------------------------------------------------
  * Function:	H5Z_filter_fletcher32
  *
  * Purpose:	Implement an I/O filter of Fletcher32 Checksum
@@ -167,7 +102,7 @@ H5Z_filter_fletcher32 (unsigned flags, size_t UNUSED cd_nelmts, const unsigned U
             UINT32DECODE(tmp_src, stored_fletcher);
 
             /* Compute checksum (can't fail) */
-            fletcher = H5Z_filter_fletcher32_compute(src,src_nbytes);
+            fletcher = H5_fletcher32(src, src_nbytes);
 
             /* The reversed checksum.  There was a bug in the calculating code of
              * the Fletcher32 checksum in the library before v1.6.3.  The checksum
@@ -201,7 +136,7 @@ H5Z_filter_fletcher32 (unsigned flags, size_t UNUSED cd_nelmts, const unsigned U
         unsigned char *dst;     /* Temporary pointer to destination buffer */
 
         /* Compute checksum (can't fail) */
-        fletcher = H5Z_filter_fletcher32_compute(src,nbytes);
+        fletcher = H5_fletcher32(src, nbytes);
 
 	if (NULL==(dst=outbuf=H5MM_malloc(nbytes+FLETCHER_LEN)))
 	    HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "unable to allocate Fletcher32 checksum destination buffer")
diff --git a/src/H5checksum.c b/src/H5checksum.c
index 3aafd3d..9ad575d 100644
--- a/src/H5checksum.c
+++ b/src/H5checksum.c
@@ -80,6 +80,11 @@
  *                  http://en.wikipedia.org/wiki/Fletcher%27s_checksum
  *              for more details, etc.
  *
+ * Note #2:     The algorithm below differs from that given in the Wikipedia
+ *              page by copying the data into 'sum1' in a more portable way
+ *              and also by initializing 'sum1' and 'sum2' to 0 instead of
+ *              0xffff (for backward compatibility reasons, mostly).
+ *
  * Return:	32-bit fletcher checksum of input buffer (can't fail)
  *
  * Programmer:	Quincey Koziol
@@ -92,7 +97,7 @@ H5_fletcher32(const void *_data, size_t _len)
 {
     const uint8_t *data = (const uint8_t *)_data;  /* Pointer to the data to be summed */
     size_t len = _len / 2;      /* Length in 16-bit words */
-    uint32_t sum1 = 0xffff, sum2 = 0xffff;
+    uint32_t sum1 = 0, sum2 = 0;
 
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_fletcher32)
 
@@ -128,6 +133,6 @@ H5_fletcher32(const void *_data, size_t _len)
     sum1 = (sum1 & 0xffff) + (sum1 >> 16);
     sum2 = (sum2 & 0xffff) + (sum2 >> 16);
 
-    FUNC_LEAVE_NOAPI(sum2 << 16 | sum1)
+    FUNC_LEAVE_NOAPI((sum2 << 16) | sum1)
 } /* end H5_fletcher32() */
 
diff --git a/test/tchecksum.c b/test/tchecksum.c
index ff49294..62c0505 100644
--- a/test/tchecksum.c
+++ b/test/tchecksum.c
@@ -57,7 +57,7 @@ test_chksum_size_one(void)
     /* Buffer w/zero(s) for data */
     HDmemset(buf, 0, sizeof(buf));
     chksum = H5_fletcher32(buf, sizeof(buf));
-    VERIFY(chksum, 0xffffffff, "H5_fletcher32");
+    VERIFY(chksum, 0, "H5_fletcher32");
 } /* test_chksum_size_one() */
 
 
@@ -79,7 +79,7 @@ test_chksum_size_two(void)
     /* Buffer w/zero(s) for data */
     HDmemset(buf, 0, sizeof(buf));
     chksum = H5_fletcher32(buf, sizeof(buf));
-    VERIFY(chksum, 0xffffffff, "H5_fletcher32");
+    VERIFY(chksum, 0, "H5_fletcher32");
 } /* test_chksum_size_two() */
 
 
@@ -101,7 +101,7 @@ test_chksum_size_three(void)
     /* Buffer w/zero(s) for data */
     HDmemset(buf, 0, sizeof(buf));
     chksum = H5_fletcher32(buf, sizeof(buf));
-    VERIFY(chksum, 0xffffffff, "H5_fletcher32");
+    VERIFY(chksum, 0, "H5_fletcher32");
 } /* test_chksum_size_three() */
 
 
@@ -123,7 +123,7 @@ test_chksum_size_four(void)
     /* Buffer w/zero(s) for data */
     HDmemset(buf, 0, sizeof(buf));
     chksum = H5_fletcher32(buf, sizeof(buf));
-    VERIFY(chksum, 0xffffffff, "H5_fletcher32");
+    VERIFY(chksum, 0, "H5_fletcher32");
 } /* test_chksum_size_four() */
 
 
@@ -149,7 +149,7 @@ test_chksum_large(void)
     /* Buffer w/zero(s) for data */
     HDmemset(large_buf, 0, sizeof(large_buf));
     chksum = H5_fletcher32(large_buf, sizeof(large_buf));
-    VERIFY(chksum, 0xffffffff, "H5_fletcher32");
+    VERIFY(chksum, 0, "H5_fletcher32");
 } /* test_chksum_large() */