[src/trunk]: src/usr.bin/sort Minor tweaks to the key generation for numeric ...

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

details:   https://anonhg.NetBSD.org/src/rev/09b0bc9de3b4
branches:  trunk
changeset: 747473:09b0bc9de3b4
user:      dsl <dsl%NetBSD.org@localhost>
date:      Wed Sep 16 20:56:38 2009 +0000

description:
Minor tweaks to the key generation for numeric fields.
Use 1's compliment for -ve numbers to avoid confitionals.

diffstat:

 usr.bin/sort/fields.c |  39 ++++++++++++++++++++++-----------------
 1 files changed, 22 insertions(+), 17 deletions(-)

diffs (116 lines):

diff -r 08e295af5dee -r 09b0bc9de3b4 usr.bin/sort/fields.c
--- a/usr.bin/sort/fields.c     Wed Sep 16 19:04:01 2009 +0000
+++ b/usr.bin/sort/fields.c     Wed Sep 16 20:56:38 2009 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fields.c,v 1.28 2009/09/10 22:02:40 dsl Exp $  */
+/*     $NetBSD: fields.c,v 1.29 2009/09/16 20:56:38 dsl Exp $  */
 
 /*-
  * Copyright (c) 2000-2003 The NetBSD Foundation, Inc.
@@ -66,7 +66,7 @@
 #include "sort.h"
 
 #ifndef lint
-__RCSID("$NetBSD: fields.c,v 1.28 2009/09/10 22:02:40 dsl Exp $");
+__RCSID("$NetBSD: fields.c,v 1.29 2009/09/16 20:56:38 dsl Exp $");
 __SCCSID("@(#)fields.c 8.1 (Berkeley) 6/6/93");
 #endif /* not lint */
 
@@ -232,21 +232,22 @@
  * exponent. These have to be ordered (-ve value, decreasing exponent),
  * zero, (+ve value, increasing exponent).
  *
- * The first byte is 0x80 for zero, 0x40 for -ve with exponent 0 and
- * 0xc0 for +ve with exponent zero.
- * This only leaves 62 byte values for +ve exponents - which isn't enough.
+ * The first byte is 0x80 for zero, 0xc0 for +ve with exponent 0.
+ * -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,
+ * This lets us sort exponents from -2^31 to +2^31.
  *
  * The mantissa is stored 2 digits per byte offset by 0x40, for negative
- * numbers the order must be reversed (they are subtracted from 0x100).
+ * numbers the order must be reversed (they are bit inverted).
  *
  * Reverse sorts are done by inverting the sign of the number.
  */
 
-#define SIGNED(reverse, value) ((reverse) ? 0x100 - (value) : (value))
-
-/* Large exponents are encoded EXP_EXC_BITS per byte */
+/* 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)
@@ -262,8 +263,12 @@
        char ch;
        unsigned int val;
        u_char *last_nz_pos;
+       u_char negate;
 
-       reverse &= R;
+       if (reverse & R)
+               negate = 0xff;
+       else
+               negate = 0;
 
        /* Give ourselves space for the key terminator */
        bufend--;
@@ -274,7 +279,7 @@
 
        SKIP_BLANKS(line);
        if (*line == '-') {     /* set the sign */
-               reverse ^= R;
+               negate ^= 0xff;
                line++;
        }
        /* eat initial zeroes */
@@ -304,11 +309,11 @@
 
        /* Maybe here we should allow for e+12 (etc) */
 
-       if (exponent < 0x3f - MAX_EXP_ENC && -exponent < 0x3f - MAX_EXP_ENC) {
+       if (exponent < 0x40 - MAX_EXP_ENC && -exponent < 0x40 - MAX_EXP_ENC) {
                /* Value ok for simple encoding */
                /* exponent 0 is 0xc0 for +ve numbers and 0x40 for -ve ones */
                exponent += 0xc0;
-               *pos++ = SIGNED(reverse, exponent);
+               *pos++ = negate ^ exponent;
        } else {
                /* Out or range for a single byte */
                int c, t;
@@ -326,12 +331,12 @@
                if (exponent < 0)
                        t = -t;
                t += 0xc0;
-               *pos++ = SIGNED(reverse, t);
+               *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++ = SIGNED(reverse, t);
+                       *pos++ = negate ^ t;
                }
        }
 
@@ -360,13 +365,13 @@
                                val += ch - '0';
                        break;
                }
-               *pos++ = SIGNED(reverse, val + 0x40);
+               *pos++ = negate ^ (val + 0x40);
                if (val != 0)
                        last_nz_pos = pos;
        }
 
        /* Add key terminator, deleting any trailing "00" */
-       *last_nz_pos++ = SIGNED(reverse, 1);
+       *last_nz_pos++ = negate;
 
        return (last_nz_pos);
 }