libgfortran/runtime/select.c

   1 /* Implement the SELECT statement for character variables.
   2    Contributed by Andy Vaught
   3
   4 This file is part of the GNU Fortran 95 runtime library (libgfortran).
   5
   6 Libgfortran is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 In addition to the permissions in the GNU General Public License, the
  12 Free Software Foundation gives you unlimited permission to link the
  13 compiled version of this file into combinations with other programs,
  14 and to distribute those combinations without any restriction coming
  15 from the use of this file.  (The General Public License restrictions
  16 do apply in other respects; for example, they cover modification of
  17 the file, and distribution when not linked into a combine
  18 executable.)
  19
  20 Libgfortran is distributed in the hope that it will be useful,
  21 but WITHOUT ANY WARRANTY; without even the implied warranty of
  22 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  23 GNU General Public License for more details.
  24
  25 You should have received a copy of the GNU General Public License
  26 along with libgfortran; see the file COPYING.  If not, write to
  27 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  28 Boston, MA 02110-1301, USA.  */
  29
  30 #include "libgfortran.h"
  31
  32 typedef struct
  33 {
  34   char *low;
  35   int low_len;
  36   char *high;
  37   int high_len;
  38   int address;
  39 }
  40 select_struct;
  41
  42 extern int select_string (select_struct *table, int table_len,
  43                           const char *selector, int selector_len);
  44 export_proto(select_string);
  45
  46
  47 /* select_string()-- Given a selector string and a table of
  48  * select_struct structures, return the address to jump to. */
  49
  50 int
  51 select_string (select_struct *table, int table_len, const char *selector,
  52                int selector_len)
  53 {
  54   select_struct *t;
  55   int i, low, high, mid;
  56   int default_jump = -1;
  57
  58   if (table_len == 0)
  59     return -1;
  60
  61   /* Record the default address if present */
  62
  63   if (table->low == NULL && table->high == NULL)
  64     {
  65       default_jump = table->address;
  66
  67       table++;
  68       table_len--;
  69       if (table_len == 0)
  70         return default_jump;
  71     }
  72
  73   /* Try the high and low bounds if present. */
  74
  75   if (table->low == NULL)
  76     {
  77       if (compare_string (table->high_len, table->high,
  78                                 selector_len, selector) >= 0)
  79         return table->address;
  80
  81       table++;
  82       table_len--;
  83       if (table_len == 0)
  84         return default_jump;
  85     }
  86
  87   t = table + table_len - 1;
  88
  89   if (t->high == NULL)
  90     {
  91       if (compare_string (t->low_len, t->low,
  92                                 selector_len, selector) <= 0)
  93         return t->address;
  94
  95       table_len--;
  96       if (table_len == 0)
  97         return default_jump;
  98     }
  99
 100   /* At this point, the only table entries are bounded entries.  Find
 101      the right entry with a binary chop. */
 102
 103   low = -1;
 104   high = table_len;
 105
 106   while (low + 1 < high)
 107     {
 108       mid = (low + high) / 2;
 109
 110       t = table + mid;
 111       i = compare_string (t->low_len, t->low, selector_len, selector);
 112
 113       if (i == 0)
 114         return t->address;
 115
 116       if (i < 0)
 117         low = mid;
 118       else
 119         high = mid;
 120     }
 121
 122   /* The string now lies between the low indeces of the now-adjacent
 123      high and low entries.  Because it is less than the low entry of
 124      'high', it can't be that one.  If low is still -1, then no
 125      entries match.  Otherwise, we have to check the high entry of
 126      'low'. */
 127
 128   if (low == -1)
 129     return default_jump;
 130
 131   t = table + low;
 132   if (compare_string (selector_len, selector,
 133                             t->high_len, t->high) <= 0)
 134     return t->address;
 135
 136   return default_jump;
 137 }