assorted-commits

[Assorted-commits] SF.net SVN: assorted: [676] sandbox/trunk/src/c/blocks.c

[<yan...@us...>]

Revision: 676
          http://assorted.svn.sourceforge.net/assorted/?rev=676&view=rev
Author:   yangzhang
Date:     2008-04-23 13:40:48 -0700 (Wed, 23 Apr 2008)

Log Message:
-----------
small sample code for performing block-segmented operations

Added Paths:
-----------
    sandbox/trunk/src/c/blocks.c

Added: sandbox/trunk/src/c/blocks.c
===================================================================
--- sandbox/trunk/src/c/blocks.c	                        (rev 0)
+++ sandbox/trunk/src/c/blocks.c	2008-04-23 20:40:48 UTC (rev 676)
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stdint.h>
+
+#define min(X,Y) ((X) < (Y) ? (X) : (Y))
+
+enum { blk = 10 };
+enum { datlen = 2 * blk };
+
+void
+f(uint32_t off, uint32_t len)
+{
+  uint32_t end = off + len;
+  uint32_t fstblk = off / blk, lstblk = (end + blk - 1) / blk;
+  printf("f(off %4d, len %4d), fstblk %2d, lstblk %2d\n", off, len, fstblk, lstblk);
+  char *p = 0;
+  for (uint32_t i = fstblk; i < lstblk; i++) {
+    uint32_t blkoff = i == fstblk ? off % blk : 0;
+    uint32_t blklen = min(end - i * blk, blk) - blkoff;
+    printf("  i %2d | blkoff %4d | blklen %4d | p %04p\n", i, blkoff, blklen, p);
+    p += blklen;
+  }
+  printf("\n");
+}
+
+int
+main()
+{
+  uint32_t starts[] = {0, 1, blk - 1, blk, blk + 1, 2 * blk};
+  uint32_t ends[]   = {0, 1, blk - 1, blk, blk + 1, 2 * blk};
+  for (int i = 0; i < sizeof starts / sizeof(*starts); i++) {
+    for (int j = 0; j < sizeof ends / sizeof(*starts); j++) {
+      f(starts[i], ends[j]);
+    }
+  }
+  return 0;
+}


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[Assorted-commits] SF.net SVN: assorted: [698] sandbox/trunk/src/c/blocks.c

[<yan...@us...>]

Revision: 698
          http://assorted.svn.sourceforge.net/assorted/?rev=698&view=rev
Author:   yangzhang
Date:     2008-05-04 00:50:13 -0700 (Sun, 04 May 2008)

Log Message:
-----------
polishing blocks.c

Modified Paths:
--------------
    sandbox/trunk/src/c/blocks.c

Modified: sandbox/trunk/src/c/blocks.c
===================================================================
--- sandbox/trunk/src/c/blocks.c	2008-05-04 07:27:22 UTC (rev 697)
+++ sandbox/trunk/src/c/blocks.c	2008-05-04 07:50:13 UTC (rev 698)
@@ -6,17 +6,39 @@
 enum { blk = 10 };
 enum { datlen = 2 * blk };
 
+/**
+ * Calculate the number of blocks in a segment of length \a i.
+ * Mathematically, this is \code ceil(i / blk) \endcode.
+ * Equivalent to \code (i - 1) / blk + 1 \endcode, but without the
+ * arithmetic underflow.
+ *
+ * E.g., with a block size of 10:
+ *
+ * \code
+ * nblocks( 0) == 0 &&
+ * nblocks( 1) == 1 && nblocks(10) == 1 &&
+ * nblocks(11) == 2 && ...
+ * \endcode
+ */
+inline uint32_t
+nblocks(uint32_t i)
+{
+  return (i + blk - 1) / blk;
+}
+
 void
 f(uint32_t off, uint32_t len)
 {
   uint32_t end = off + len;
-  uint32_t fstblk = off / blk, lstblk = (end + blk - 1) / blk;
-  printf("f(off %4d, len %4d), fstblk %2d, lstblk %2d\n", off, len, fstblk, lstblk);
+  uint32_t fstblk = off / blk, lstblk = nblocks(end);
+  printf("f(off %4d, len %4d), fstblk %2d, lstblk %2d\n",
+         off, len, fstblk, lstblk);
   char *p = 0;
   for (uint32_t i = fstblk; i < lstblk; i++) {
     uint32_t blkoff = i == fstblk ? off % blk : 0;
     uint32_t blklen = min(end - i * blk, blk) - blkoff;
-    printf("  i %2d | blkoff %4d | blklen %4d | p %04p\n", i, blkoff, blklen, p);
+    printf("  i %2d | blkoff %4d | blklen %4d | p %04p\n",
+           i, blkoff, blklen, p);
     p += blklen;
   }
   printf("\n");


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