1/* contrib/arm-neon/linux.c
  2 *
  3 * Copyright (c) 2014 Glenn Randers-Pehrson
  4 * Written by John Bowler, 2014.
  5 * Last changed in libpng 1.6.16 [December 22, 2014]
  6 *
  7 * This code is released under the libpng license.
  8 * For conditions of distribution and use, see the disclaimer
  9 * and license in png.h
 10 *
 11 * SEE contrib/arm-neon/README before reporting bugs
 12 *
 13 * STATUS: SUPPORTED
 14 * BUG REPORTS: png-mng-implement@sourceforge.net
 15 *
 16 * png_have_neon implemented for Linux by reading the widely available
 17 * pseudo-file /proc/cpuinfo.
 18 *
 19 * This code is strict ANSI-C and is probably moderately portable; it does
 20 * however use <stdio.h> and it assumes that /proc/cpuinfo is never localized.
 21 */
 22#include <stdio.h>
 23
 24static int
 25png_have_neon(png_structp png_ptr)
 26{
 27   FILE *f = fopen("/proc/cpuinfo", "rb");
 28
 29   if (f != NULL)
 30   {
 31      /* This is a simple state machine which reads the input byte-by-byte until
 32       * it gets a match on the 'neon' feature or reaches the end of the stream.
 33       */
 34      static const char ch_feature[] = { 70, 69, 65, 84, 85, 82, 69, 83 };
 35      static const char ch_neon[] = { 78, 69, 79, 78 };
 36
 37      enum
 38      {
 39         StartLine, Feature, Colon, StartTag, Neon, HaveNeon, SkipTag, SkipLine
 40      }  state;
 41      int counter;
 42
 43      for (state=StartLine, counter=0;;)
 44      {
 45         int ch = fgetc(f);
 46
 47         if (ch == EOF)
 48         {
 49            /* EOF means error or end-of-file, return false; neon at EOF is
 50             * assumed to be a mistake.
 51             */
 52            fclose(f);
 53            return 0;
 54         }
 55
 56         switch (state)
 57         {
 58            case StartLine:
 59               /* Match spaces at the start of line */
 60               if (ch <= 32) /* skip control characters and space */
 61                  break;
 62
 63               counter=0;
 64               state = Feature;
 65               /* FALL THROUGH */
 66
 67            case Feature:
 68               /* Match 'FEATURE', ASCII case insensitive. */
 69               if ((ch & ~0x20) == ch_feature[counter])
 70               {
 71                  if (++counter == (sizeof ch_feature))
 72                     state = Colon;
 73                  break;
 74               }
 75               
 76               /* did not match 'feature' */
 77               state = SkipLine;
 78               /* FALL THROUGH */
 79
 80            case SkipLine:
 81            skipLine:
 82               /* Skip everything until we see linefeed or carriage return */
 83               if (ch != 10 && ch != 13)
 84                  break;
 85
 86               state = StartLine;
 87               break;
 88
 89            case Colon:
 90               /* Match any number of space or tab followed by ':' */
 91               if (ch == 32 || ch == 9)
 92                  break;
 93
 94               if (ch == 58) /* i.e. ':' */
 95               {
 96                  state = StartTag;
 97                  break;
 98               }
 99
100               /* Either a bad line format or a 'feature' prefix followed by
101                * other characters.
102                */
103               state = SkipLine;
104               goto skipLine;
105
106            case StartTag:
107               /* Skip space characters before a tag */
108               if (ch == 32 || ch == 9)
109                  break;
110
111               state = Neon;
112               counter = 0;
113               /* FALL THROUGH */
114
115            case Neon:
116               /* Look for 'neon' tag */
117               if ((ch & ~0x20) == ch_neon[counter])
118               {
119                  if (++counter == (sizeof ch_neon))
120                     state = HaveNeon;
121                  break;
122               }
123
124               state = SkipTag;
125               /* FALL THROUGH */
126
127            case SkipTag:
128               /* Skip non-space characters */
129               if (ch == 10 || ch == 13)
130                  state = StartLine;
131
132               else if (ch == 32 || ch == 9)
133                  state = StartTag;
134               break;
135
136            case HaveNeon:
137               /* Have seen a 'neon' prefix, but there must be a space or new
138                * line character to terminate it.
139                */
140               if (ch == 10 || ch == 13 || ch == 32 || ch == 9)
141               {
142                  fclose(f);
143                  return 1;
144               }
145
146               state = SkipTag;
147               break;
148
149            default:
150               png_error(png_ptr, "png_have_neon: internal error (bug)");
151         }
152      }
153   }
154
155#ifdef PNG_WARNINGS_SUPPORTED
156   else
157      png_warning(png_ptr, "/proc/cpuinfo open failed");
158#endif
159
160   return 0;
161}