int*_t are guaranteed to use two's complete ... clean, understandable, and wonderful code

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/libkeccak/spec.h b/src/libkeccak/spec.h
index cccd27c..3e14f8e 100644
--- a/src/libkeccak/spec.h
+++ b/src/libkeccak/spec.h
@@ -20,6 +20,7 @@
 #define LIBKECCAK_SPEC_H  1
 
 
+#include <stdint.h>
 #include <limits.h>
 
 
@@ -167,7 +168,7 @@ static inline __attribute__((nonnull, nothrow, unused, warn_unused_result, pure)
 int libkeccak_spec_check(const libkeccak_spec_t* restrict spec)
 {
   long state_size = spec->capacity + spec->bitrate;
-  long word_size = state_size / 25, n_word_size;
+  int_fast32_t word_size = (int_fast32_t)(state_size / 25);
   if (spec->bitrate <= 0)   return LIBKECCAK_SPEC_ERROR_BITRATE_NONPOSITIVE;
   if (spec->bitrate % 8)    return LIBKECCAK_SPEC_ERROR_BITRATE_MOD_8;
   if (spec->capacity <= 0)  return LIBKECCAK_SPEC_ERROR_CAPACITY_NONPOSITIVE;
@@ -177,10 +178,11 @@ int libkeccak_spec_check(const libkeccak_spec_t* restrict spec)
   if (state_size % 25)      return LIBKECCAK_SPEC_ERROR_STATE_MOD_25;
   if (word_size % 8)        return LIBKECCAK_SPEC_ERROR_WORD_MOD_8;
   
-  /* This is a portable implementation of `(x & -x) != x` which assumes
-   * two's complement, which of course is always satisfied by GCC, but anyway... */
-  n_word_size = ((~word_size) ^ (LONG_MIN & ~LONG_MAX)) + 1;
-  if ((word_size & n_word_size) != word_size)
+  /* `(x & -x) != x` assumes two's complement, which of course is always
+   * satisfied by GCC, however C99 guarantees that `int_fast32_t` exists,
+   * and it is basically the same thing as `long int`; with one important
+   * difference: it is guaranteed to use two's complement. */
+  if ((word_size & -word_size) != word_size)
     return LIBKECCAK_SPEC_ERROR_WORD_NON_2_POTENT;
   
   return 0;