src/tac-pipe.c

   1 /* FIXME */
   2 #include <assert.h>
   3
   4 /* FIXME: this is small for testing */
   5 #define BUFFER_SIZE (8)
   6
   7 #define LEN(X, I) ((X)->p[(I)].one_past_end - (X)->p[(I)].start)
   8 #define EMPTY(X) ((X)->n_bufs == 1 && LEN (X, 0) == 0)
   9
  10 #define ONE_PAST_END(X, I) ((X)->p[(I)].one_past_end)
  11
  12 struct Line_ptr
  13 {
  14   size_t i;
  15   char *ptr;
  16 };
  17 typedef struct Line_ptr Line_ptr;
  18
  19 struct B_pair
  20 {
  21   char *start;
  22   char *one_past_end;
  23 };
  24
  25 struct Buf
  26 {
  27   size_t n_bufs;
  28   struct obstack obs;
  29   struct B_pair *p;
  30 };
  31 typedef struct Buf Buf;
  32
  33 static int
  34 buf_init_from_stdin (Buf *x, int eol_byte)
  35 {
  36   int last_byte_is_eol_byte = 1;
  37   int fail = 0;
  38
  39 #define OBS (&(x->obs))
  40   obstack_init (OBS);
  41
  42   while (1)
  43     {
  44       char *buf = (char *) malloc (BUFFER_SIZE);
  45       int bytes_read;
  46
  47       if (buf == NULL)
  48         {
  49           /* Fall back on the code that relies on a temporary file.
  50              Write all buffers to that file and free them.  */
  51           /* FIXME */
  52           fail = 1;
  53           break;
  54         }
  55       bytes_read = full_read (STDIN_FILENO, buf, BUFFER_SIZE);
  56       if (bytes_read < 0)
  57         error (EXIT_FAILURE, errno, _("read error"));
  58
  59       {
  60         struct B_pair bp;
  61         bp.start = buf;
  62         bp.one_past_end = buf + bytes_read;
  63         obstack_grow (OBS, &bp, sizeof (bp));
  64       }
  65
  66       if (bytes_read > 0)
  67         last_byte_is_eol_byte = (buf[bytes_read - 1] == eol_byte);
  68
  69       if (bytes_read < BUFFER_SIZE)
  70         break;
  71     }
  72
  73   if (!fail)
  74     {
  75       /* If the file was non-empty and lacked an EOL_BYTE at its end,
  76          then add a buffer containing just that one byte.  */
  77       if (!last_byte_is_eol_byte)
  78         {
  79           char *buf = malloc (1);
  80           if (buf == NULL)
  81             {
  82               /* FIXME: just like above */
  83               fail = 1;
  84             }
  85           else
  86             {
  87               struct B_pair bp;
  88               *buf = eol_byte;
  89               bp.start = buf;
  90               bp.one_past_end = buf + 1;
  91               obstack_grow (OBS, &bp, sizeof (bp));
  92             }
  93         }
  94     }
  95
  96   x->n_bufs = obstack_object_size (OBS) / sizeof (x->p[0]);
  97   x->p = (struct B_pair *) obstack_finish (OBS);
  98
  99   /* If there are two or more buffers and the last buffer is empty,
 100      then free the last one and decrement the buffer count.  */
 101   if (x->n_bufs >= 2
 102       && x->p[x->n_bufs - 1].start == x->p[x->n_bufs - 1].one_past_end)
 103     free (x->p[--(x->n_bufs)].start);
 104
 105   return fail;
 106 }
 107
 108 static void
 109 buf_free (Buf *x)
 110 {
 111   int i;
 112   for (i = 0; i < x->n_bufs; i++)
 113     free (x->p[i].start);
 114   obstack_free (OBS, NULL);
 115 }
 116
 117 Line_ptr
 118 line_ptr_decrement (const Buf *x, const Line_ptr *lp)
 119 {
 120   Line_ptr lp_new;
 121
 122   if (lp->ptr > x->p[lp->i].start)
 123     {
 124       lp_new.i = lp->i;
 125       lp_new.ptr = lp->ptr - 1;
 126     }
 127   else
 128     {
 129       assert (lp->i > 0);
 130       lp_new.i = lp->i - 1;
 131       lp_new.ptr = ONE_PAST_END (x, lp->i - 1) - 1;
 132     }
 133   return lp_new;
 134 }
 135
 136 Line_ptr
 137 line_ptr_increment (const Buf *x, const Line_ptr *lp)
 138 {
 139   Line_ptr lp_new;
 140
 141   assert (lp->ptr <= ONE_PAST_END (x, lp->i) - 1);
 142   if (lp->ptr < ONE_PAST_END (x, lp->i) - 1)
 143     {
 144       lp_new.i = lp->i;
 145       lp_new.ptr = lp->ptr + 1;
 146     }
 147   else
 148     {
 149       assert (lp->i < x->n_bufs - 1);
 150       lp_new.i = lp->i + 1;
 151       lp_new.ptr = x->p[lp->i + 1].start;
 152     }
 153   return lp_new;
 154 }
 155
 156 static int
 157 find_bol (const Buf *x,
 158           const Line_ptr *last_bol, Line_ptr *new_bol, char eol_byte)
 159 {
 160   int i;
 161   Line_ptr tmp;
 162   char *last_bol_ptr;
 163
 164   if (last_bol->ptr == x->p[0].start)
 165     return 0;
 166
 167   tmp = line_ptr_decrement (x, last_bol);
 168   last_bol_ptr = tmp.ptr;
 169   i = tmp.i;
 170   while (1)
 171     {
 172       char *nl = memrchr (x->p[i].start, last_bol_ptr, eol_byte);
 173       if (nl)
 174         {
 175           Line_ptr nl_pos;
 176           nl_pos.i = i;
 177           nl_pos.ptr = nl;
 178           *new_bol = line_ptr_increment (x, &nl_pos);
 179           return 1;
 180         }
 181
 182       if (i <= 0)
 183         break;
 184
 185       --i;
 186       last_bol_ptr = ONE_PAST_END (x, i);
 187     }
 188
 189   /* If last_bol->ptr didn't point at the first byte of X, then reaching
 190      this point means that we're about to return the line that is at the
 191      beginning of X.  */
 192   if (last_bol->ptr != x->p[0].start)
 193     {
 194       new_bol->i = 0;
 195       new_bol->ptr = x->p[0].start;
 196       return 1;
 197     }
 198
 199   return 0;
 200 }
 201
 202 static void
 203 print_line (FILE *out_stream, const Buf *x,
 204             const Line_ptr *bol, const Line_ptr *bol_next)
 205 {
 206   int i;
 207   for (i = bol->i; i <= bol_next->i; i++)
 208     {
 209       char *a = (i == bol->i ? bol->ptr : x->p[i].start);
 210       char *b = (i == bol_next->i ? bol_next->ptr : ONE_PAST_END (x, i));
 211       fwrite (a, 1, b - a, out_stream);
 212     }
 213 }
 214
 215 static int
 216 tac_mem ()
 217 {
 218   Buf x;
 219   Line_ptr bol;
 220   char eol_byte = '\n';
 221   int fail;
 222
 223   fail = buf_init_from_stdin (&x, eol_byte);
 224   if (fail)
 225     {
 226       buf_free (&x);
 227       return 1;
 228     }
 229
 230   /* Special case the empty file.  */
 231   if (EMPTY (&x))
 232     return 0;
 233
 234   /* Initially, point at one past the last byte of the file.  */
 235   bol.i = x.n_bufs - 1;
 236   bol.ptr = ONE_PAST_END (&x, bol.i);
 237
 238   while (1)
 239     {
 240       Line_ptr new_bol;
 241       int found = find_bol (&x, &bol, &new_bol, eol_byte);
 242       if (!found)
 243         break;
 244       print_line (stdout, &x, &new_bol, &bol);
 245       bol = new_bol;
 246     }
 247   return 0;
 248 }