[src/trunk]: src/usr.bin/sort When encoding numbers, we can use all 8 bits fo...

[dsl <dsl%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/9b271e175f8a
branches:  trunk
changeset: 747985:9b271e175f8a
user:      dsl <dsl%NetBSD.org@localhost>
date:      Wed Oct 07 21:02:57 2009 +0000

description:
When encoding numbers, we can use all 8 bits for exponent values.

diffstat:

 usr.bin/sort/fields.c |  39 ++++++++++++++-------------------------
 1 files changed, 14 insertions(+), 25 deletions(-)

diffs (83 lines):

diff -r 144d022a1d8d -r 9b271e175f8a usr.bin/sort/fields.c
--- a/usr.bin/sort/fields.c     Wed Oct 07 20:59:09 2009 +0000
+++ b/usr.bin/sort/fields.c     Wed Oct 07 21:02:57 2009 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fields.c,v 1.29 2009/09/16 20:56:38 dsl Exp $  */
+/*     $NetBSD: fields.c,v 1.30 2009/10/07 21:02:57 dsl Exp $  */
 
 /*-
  * Copyright (c) 2000-2003 The NetBSD Foundation, Inc.
@@ -66,7 +66,7 @@
 #include "sort.h"
 
 #ifndef lint
-__RCSID("$NetBSD: fields.c,v 1.29 2009/09/16 20:56:38 dsl Exp $");
+__RCSID("$NetBSD: fields.c,v 1.30 2009/10/07 21:02:57 dsl Exp $");
 __SCCSID("@(#)fields.c 8.1 (Berkeley) 6/6/93");
 #endif /* not lint */
 
@@ -236,8 +236,8 @@
  * -ve values are the 1's compliments (so 0x7f isn't used!).
  *
  * This only leaves 63 byte values for +ve exponents - which isn't enough.
- * The largest 5 exponent values are used to hold a byte count of the
- * number of following bytes that contain 7 exponent bits per byte,
+ * The largest 4 exponent values are used to hold a byte count of the
+ * number of following bytes that contain 8 exponent bits per byte,
  * This lets us sort exponents from -2^31 to +2^31.
  *
  * The mantissa is stored 2 digits per byte offset by 0x40, for negative
@@ -245,13 +245,7 @@
  *
  * Reverse sorts are done by inverting the sign of the number.
  */
-
-/* Large exponents are encoded EXP_EXC_BITS per byte, MAX_EXP_ENC is the
- * number of bytes required to contain an exponent. */
-#define EXP_ENC_BITS 7
-#define EXP_ENC_VAL  (1 << EXP_ENC_BITS)
-#define EXP_ENC_MASK (EXP_ENC_VAL - 1)
-#define MAX_EXP_ENC  ((int)(sizeof(int) * 8 + (EXP_ENC_BITS-1))/EXP_ENC_BITS)
+#define MAX_EXP_ENC  ((int)sizeof(int))
 
 static u_char *
 number(u_char *pos, const u_char *bufend, u_char *line, u_char *lineend,
@@ -318,29 +312,24 @@
                /* Out or range for a single byte */
                int c, t;
                t = exponent > 0 ? exponent : -exponent;
-               /* Count how many 7-bit blocks are needed */
+               /* Count how many 8-bit bytes are needed */
                for (c = 0; ; c++) {
-                       t /= EXP_ENC_VAL;
+                       t >>= 8;
                        if (t == 0)
                                break;
                }
-               /* 'c' better be 0..4 here - but probably 0..2 */
-               t = c;
+               /* 'c' better be 0..3 here - but probably 0..1 */
                /* Offset just outside valid range */
-               t += 0x40 - MAX_EXP_ENC;
+               t = c + 0x40 - MAX_EXP_ENC;
                if (exponent < 0)
                        t = -t;
-               t += 0xc0;
-               *pos++ = negate ^ t;
-               /* now add each 7-bit block (offset 0x40..0xbf) */
-               for (; c >= 0; c--) {
-                       t = exponent >> (c * EXP_ENC_BITS);
-                       t = (t & EXP_ENC_MASK) + 0x40;
-                       *pos++ = negate ^ t;
-               }
+               *pos++ = negate ^ (t + 0xc0);
+               /* now add each byte, most significant first */
+               for (; c >= 0; c--)
+                       *pos++ = negate ^ (exponent >> (c * 8));
        }
 
-       /* Now add mantissa, 2 digits per byte */
+       /* Finally add mantissa, 2 digits per byte */
        for (last_nz_pos = pos; line < lineend; ) {
                if (pos >= bufend)
                        return NULL;