akr	2010-03-04 23:20:49 +0900 (Thu, 04 Mar 2010)

  New Revision: 26818

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=26818

  Log:
    add comment.

  Modified files:
    trunk/bignum.c

Index: bignum.c
===================================================================
--- bignum.c	(revision 26817)
+++ bignum.c	(revision 26818)
@@ -308,6 +308,19 @@
 # error unexpected SIZEOF_LONG : SIZEOF_BDIGITS ratio
 #endif
 
+/*
+ * buf is an array of long integers.
+ * buf is ordered from least significant word to most significant word.
+ * buf[0] is the least significant word and
+ * buf[num_longs-1] is the most significant word.
+ * This means words in buf is little endian.
+ * However each word in buf is native endian.
+ * (buf[i]&1) is the least significant bit and
+ * (buf[i]&(1<<(SIZEOF_LONG*CHAR_BIT-1))) is the most significant bit
+ * for each 0 <= i < num_longs.
+ * So buf is little endian at whole on a little endian machine.
+ * But buf is mixed endian on a big endian machine.
+ */
 void
 rb_big_pack(VALUE val, unsigned long *buf, long num_longs)
 {
@@ -349,6 +362,7 @@
     }
 }
 
+/* See rb_big_pack comment for endianness of buf. */
 VALUE
 rb_big_unpack(unsigned long *buf, long num_longs)
 {

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