usr.bin/telnet/ring.c

   1 /*
   2  * Copyright (c) 1988, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * @(#)ring.c   8.2 (Berkeley) 5/30/95
  34  * $FreeBSD: src/usr.bin/telnet/ring.c,v 1.3.6.1 2002/04/13 11:07:13 markm Exp $
  35  * $DragonFly: src/usr.bin/telnet/ring.c,v 1.2 2003/06/17 04:29:32 dillon Exp $
  36  */
  37
  38 /*
  39  * This defines a structure for a ring buffer.
  40  *
  41  * The circular buffer has two parts:
  42  *(((
  43  *      full:   [consume, supply)
  44  *      empty:  [supply, consume)
  45  *]]]
  46  *
  47  */
  48
  49 #include        <errno.h>
  50 #include        <stdio.h>
  51 #include        <string.h>
  52
  53 #ifdef  size_t
  54 #undef  size_t
  55 #endif
  56
  57 #include        <sys/types.h>
  58 #ifndef FILIO_H
  59 #include        <sys/ioctl.h>
  60 #endif
  61 #include        <sys/socket.h>
  62
  63 #include        "ring.h"
  64 #include        "general.h"
  65
  66 /* Internal macros */
  67
  68 #if     !defined(MIN)
  69 #define MIN(a,b)        (((a)<(b))? (a):(b))
  70 #endif  /* !defined(MIN) */
  71
  72 #define ring_subtract(d,a,b)    (((a)-(b) >= 0)? \
  73                                         (a)-(b): (((a)-(b))+(d)->size))
  74
  75 #define ring_increment(d,a,c)   (((a)+(c) < (d)->top)? \
  76                                         (a)+(c) : (((a)+(c))-(d)->size))
  77
  78 #define ring_decrement(d,a,c)   (((a)-(c) >= (d)->bottom)? \
  79                                         (a)-(c) : (((a)-(c))-(d)->size))
  80
  81
  82 /*
  83  * The following is a clock, used to determine full, empty, etc.
  84  *
  85  * There is some trickiness here.  Since the ring buffers are initialized
  86  * to ZERO on allocation, we need to make sure, when interpreting the
  87  * clock, that when the times are EQUAL, then the buffer is FULL.
  88  */
  89 static u_long ring_clock = 0;
  90
  91
  92 #define ring_empty(d) (((d)->consume == (d)->supply) && \
  93                                 ((d)->consumetime >= (d)->supplytime))
  94 #define ring_full(d) (((d)->supply == (d)->consume) && \
  95                                 ((d)->supplytime > (d)->consumetime))
  96
  97 /* Buffer state transition routines */
  98
  99 int
 100 ring_init(Ring *ring, unsigned char *buffer, int count)
 101 {
 102     memset((char *)ring, 0, sizeof *ring);
 103
 104     ring->size = count;
 105
 106     ring->supply = ring->consume = ring->bottom = buffer;
 107
 108     ring->top = ring->bottom+ring->size;
 109
 110
 111     return 1;
 112 }
 113
 114 /* Mark routines */
 115
 116 /*
 117  * Mark the most recently supplied byte.
 118  */
 119
 120 void
 121 ring_mark(Ring *ring)
 122 {
 123     ring->mark = ring_decrement(ring, ring->supply, 1);
 124 }
 125
 126 /*
 127  * Is the ring pointing to the mark?
 128  */
 129
 130 int
 131 ring_at_mark(Ring *ring)
 132 {
 133     if (ring->mark == ring->consume) {
 134         return 1;
 135     } else {
 136         return 0;
 137     }
 138 }
 139
 140 /*
 141  * Clear any mark set on the ring.
 142  */
 143
 144 void
 145 ring_clear_mark(Ring *ring)
 146 {
 147     ring->mark = 0;
 148 }
 149
 150 /*
 151  * Add characters from current segment to ring buffer.
 152  */
 153 void
 154 ring_supplied(Ring *ring, int count)
 155 {
 156     ring->supply = ring_increment(ring, ring->supply, count);
 157     ring->supplytime = ++ring_clock;
 158 }
 159
 160 /*
 161  * We have just consumed "c" bytes.
 162  */
 163 void
 164 ring_consumed(Ring *ring, int count)
 165 {
 166     if (count == 0)     /* don't update anything */
 167         return;
 168
 169     if (ring->mark &&
 170                 (ring_subtract(ring, ring->mark, ring->consume) < count)) {
 171         ring->mark = 0;
 172     }
 173     ring->consume = ring_increment(ring, ring->consume, count);
 174     ring->consumetime = ++ring_clock;
 175     /*
 176      * Try to encourage "ring_empty_consecutive()" to be large.
 177      */
 178     if (ring_empty(ring)) {
 179         ring->consume = ring->supply = ring->bottom;
 180     }
 181 }
 182
 183
 184
 185 /* Buffer state query routines */
 186
 187
 188 /* Number of bytes that may be supplied */
 189 int
 190 ring_empty_count(Ring *ring)
 191 {
 192     if (ring_empty(ring)) {     /* if empty */
 193             return ring->size;
 194     } else {
 195         return ring_subtract(ring, ring->consume, ring->supply);
 196     }
 197 }
 198
 199 /* number of CONSECUTIVE bytes that may be supplied */
 200 int
 201 ring_empty_consecutive(Ring *ring)
 202 {
 203     if ((ring->consume < ring->supply) || ring_empty(ring)) {
 204                             /*
 205                              * if consume is "below" supply, or empty, then
 206                              * return distance to the top
 207                              */
 208         return ring_subtract(ring, ring->top, ring->supply);
 209     } else {
 210                                     /*
 211                                      * else, return what we may.
 212                                      */
 213         return ring_subtract(ring, ring->consume, ring->supply);
 214     }
 215 }
 216
 217 /* Return the number of bytes that are available for consuming
 218  * (but don't give more than enough to get to cross over set mark)
 219  */
 220
 221 int
 222 ring_full_count(Ring *ring)
 223 {
 224     if ((ring->mark == 0) || (ring->mark == ring->consume)) {
 225         if (ring_full(ring)) {
 226             return ring->size;  /* nothing consumed, but full */
 227         } else {
 228             return ring_subtract(ring, ring->supply, ring->consume);
 229         }
 230     } else {
 231         return ring_subtract(ring, ring->mark, ring->consume);
 232     }
 233 }
 234
 235 /*
 236  * Return the number of CONSECUTIVE bytes available for consuming.
 237  * However, don't return more than enough to cross over set mark.
 238  */
 239 int
 240 ring_full_consecutive(Ring *ring)
 241 {
 242     if ((ring->mark == 0) || (ring->mark == ring->consume)) {
 243         if ((ring->supply < ring->consume) || ring_full(ring)) {
 244             return ring_subtract(ring, ring->top, ring->consume);
 245         } else {
 246             return ring_subtract(ring, ring->supply, ring->consume);
 247         }
 248     } else {
 249         if (ring->mark < ring->consume) {
 250             return ring_subtract(ring, ring->top, ring->consume);
 251         } else {        /* Else, distance to mark */
 252             return ring_subtract(ring, ring->mark, ring->consume);
 253         }
 254     }
 255 }
 256
 257 /*
 258  * Move data into the "supply" portion of of the ring buffer.
 259  */
 260 void
 261 ring_supply_data(Ring *ring, unsigned char *buffer, int count)
 262 {
 263     int i;
 264
 265     while (count) {
 266         i = MIN(count, ring_empty_consecutive(ring));
 267         memcpy(ring->supply, buffer, i);
 268         ring_supplied(ring, i);
 269         count -= i;
 270         buffer += i;
 271     }
 272 }
 273