src/tac-pipe.c

   1 /* tac from a pipe.
   2
   3    Copyright (C) 1997-2023 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* FIXME */
  19 #include <assert.h>
  20
  21 #include "die.h"
  22
  23 /* FIXME: this is small for testing */
  24 #define BUFFER_SIZE (8)
  25
  26 #define LEN(X, I) ((X)->p[(I)].one_past_end - (X)->p[(I)].start)
  27 #define EMPTY(X) ((X)->n_bufs == 1 && LEN (X, 0) == 0)
  28
  29 #define ONE_PAST_END(X, I) ((X)->p[(I)].one_past_end)
  30
  31 struct Line_ptr
  32 {
  33   size_t i;
  34   char *ptr;
  35 };
  36 typedef struct Line_ptr Line_ptr;
  37
  38 struct B_pair
  39 {
  40   char *start;
  41   char *one_past_end;
  42 };
  43
  44 struct Buf
  45 {
  46   size_t n_bufs;
  47   struct obstack obs;
  48   struct B_pair *p;
  49 };
  50 typedef struct Buf Buf;
  51
  52 static bool
  53 buf_init_from_stdin (Buf *x, char eol_byte)
  54 {
  55   bool last_byte_is_eol_byte = true;
  56   bool ok = true;
  57
  58 #define OBS (&(x->obs))
  59   obstack_init (OBS);
  60
  61   while (true)
  62     {
  63       char *buf = (char *) malloc (BUFFER_SIZE);
  64       size_t bytes_read;
  65
  66       if (buf == NULL)
  67         {
  68           /* Fall back on the code that relies on a temporary file.
  69              Write all buffers to that file and free them.  */
  70           /* FIXME */
  71           ok = false;
  72           break;
  73         }
  74       bytes_read = full_read (STDIN_FILENO, buf, BUFFER_SIZE);
  75       if (bytes_read != buffer_size && errno != 0)
  76         die (EXIT_FAILURE, errno, _("read error"));
  77
  78       {
  79         struct B_pair bp;
  80         bp.start = buf;
  81         bp.one_past_end = buf + bytes_read;
  82         obstack_grow (OBS, &bp, sizeof (bp));
  83       }
  84
  85       if (bytes_read != 0)
  86         last_byte_is_eol_byte = (buf[bytes_read - 1] == eol_byte);
  87
  88       if (bytes_read < BUFFER_SIZE)
  89         break;
  90     }
  91
  92   if (ok)
  93     {
  94       /* If the file was non-empty and lacked an EOL_BYTE at its end,
  95          then add a buffer containing just that one byte.  */
  96       if (!last_byte_is_eol_byte)
  97         {
  98           char *buf = malloc (1);
  99           if (buf == NULL)
 100             {
 101               /* FIXME: just like above */
 102               ok = false;
 103             }
 104           else
 105             {
 106               struct B_pair bp;
 107               *buf = eol_byte;
 108               bp.start = buf;
 109               bp.one_past_end = buf + 1;
 110               obstack_grow (OBS, &bp, sizeof (bp));
 111             }
 112         }
 113     }
 114
 115   x->n_bufs = obstack_object_size (OBS) / sizeof (x->p[0]);
 116   x->p = (struct B_pair *) obstack_finish (OBS);
 117
 118   /* If there are two or more buffers and the last buffer is empty,
 119      then free the last one and decrement the buffer count.  */
 120   if (x->n_bufs >= 2
 121       && x->p[x->n_bufs - 1].start == x->p[x->n_bufs - 1].one_past_end)
 122     free (x->p[--(x->n_bufs)].start);
 123
 124   return ok;
 125 }
 126
 127 static void
 128 buf_free (Buf *x)
 129 {
 130   for (size_t i = 0; i < x->n_bufs; i++)
 131     free (x->p[i].start);
 132   obstack_free (OBS, NULL);
 133 }
 134
 135 Line_ptr
 136 line_ptr_decrement (const Buf *x, const Line_ptr *lp)
 137 {
 138   Line_ptr lp_new;
 139
 140   if (lp->ptr > x->p[lp->i].start)
 141     {
 142       lp_new.i = lp->i;
 143       lp_new.ptr = lp->ptr - 1;
 144     }
 145   else
 146     {
 147       assert (lp->i > 0);
 148       lp_new.i = lp->i - 1;
 149       lp_new.ptr = ONE_PAST_END (x, lp->i - 1) - 1;
 150     }
 151   return lp_new;
 152 }
 153
 154 Line_ptr
 155 line_ptr_increment (const Buf *x, const Line_ptr *lp)
 156 {
 157   Line_ptr lp_new;
 158
 159   assert (lp->ptr <= ONE_PAST_END (x, lp->i) - 1);
 160   if (lp->ptr < ONE_PAST_END (x, lp->i) - 1)
 161     {
 162       lp_new.i = lp->i;
 163       lp_new.ptr = lp->ptr + 1;
 164     }
 165   else
 166     {
 167       assert (lp->i < x->n_bufs - 1);
 168       lp_new.i = lp->i + 1;
 169       lp_new.ptr = x->p[lp->i + 1].start;
 170     }
 171   return lp_new;
 172 }
 173
 174 static bool
 175 find_bol (const Buf *x,
 176           const Line_ptr *last_bol, Line_ptr *new_bol, char eol_byte)
 177 {
 178   size_t i;
 179   Line_ptr tmp;
 180   char *last_bol_ptr;
 181
 182   if (last_bol->ptr == x->p[0].start)
 183     return false;
 184
 185   tmp = line_ptr_decrement (x, last_bol);
 186   last_bol_ptr = tmp.ptr;
 187   i = tmp.i;
 188   while (true)
 189     {
 190       char *nl = memrchr (x->p[i].start, last_bol_ptr, eol_byte);
 191       if (nl)
 192         {
 193           Line_ptr nl_pos;
 194           nl_pos.i = i;
 195           nl_pos.ptr = nl;
 196           *new_bol = line_ptr_increment (x, &nl_pos);
 197           return true;
 198         }
 199
 200       if (i == 0)
 201         break;
 202
 203       --i;
 204       last_bol_ptr = ONE_PAST_END (x, i);
 205     }
 206
 207   /* If last_bol->ptr didn't point at the first byte of X, then reaching
 208      this point means that we're about to return the line that is at the
 209      beginning of X.  */
 210   if (last_bol->ptr != x->p[0].start)
 211     {
 212       new_bol->i = 0;
 213       new_bol->ptr = x->p[0].start;
 214       return true;
 215     }
 216
 217   return false;
 218 }
 219
 220 static void
 221 print_line (FILE *out_stream, const Buf *x,
 222             const Line_ptr *bol, const Line_ptr *bol_next)
 223 {
 224   for (size_t i = bol->i; i <= bol_next->i; i++)
 225     {
 226       char *a = (i == bol->i ? bol->ptr : x->p[i].start);
 227       char *b = (i == bol_next->i ? bol_next->ptr : ONE_PAST_END (x, i));
 228       fwrite (a, 1, b - a, out_stream);
 229     }
 230 }
 231
 232 static bool
 233 tac_mem ()
 234 {
 235   Buf x;
 236   Line_ptr bol;
 237   char eol_byte = '\n';
 238
 239   if (! buf_init_from_stdin (&x, eol_byte))
 240     {
 241       buf_free (&x);
 242       return false;
 243     }
 244
 245   /* Special case the empty file.  */
 246   if (EMPTY (&x))
 247     return true;
 248
 249   /* Initially, point at one past the last byte of the file.  */
 250   bol.i = x.n_bufs - 1;
 251   bol.ptr = ONE_PAST_END (&x, bol.i);
 252
 253   while (true)
 254     {
 255       Line_ptr new_bol;
 256       if (! find_bol (&x, &bol, &new_bol, eol_byte))
 257         break;
 258       print_line (stdout, &x, &new_bol, &bol);
 259       bol = new_bol;
 260     }
 261   return true;
 262 }