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}
162