[Nauty] Big endian sha256

[Jerry James]

I tried building nauty 2.9.0 for Fedora.  The tests failed on our s390x
(big endian) builder because the code in nausha.c assumes little
endianness.  Applying the following patch led to a successful build.  The
endian.h header is part of the POSIX specification, but if you build for
non-POSIX systems, you might want to use the AC_C_BIGENDIAN macro in
configure.ac instead.  It defines WORDS_BIGENDIAN on big endian machines.

--- a/nausha.c
+++ b/nausha.c
@@ -1,6 +1,7 @@
 /* nausha.c version 1.0; B D McKay, January 2025 */

 #include "nausha.h"
+#include <endian.h>

 /****************************************************************************
 * This implementation of SHA256 is by Brad Conte, released to public
domain.
@@ -174,6 +175,7 @@ sha256_final(SHA256_CTX *ctx, nsword8 ha
     // Since this implementation uses little endian byte ordering and SHA
uses big endian,
     // reverse all the bytes when copying the final state to the output
hash.
     for (i = 0; i < 4; ++i) {
+#if __BYTE_ORDER == __LITTLE_ENDIAN
         hash[i]      = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
         hash[i + 4]  = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
         hash[i + 8]  = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
@@ -182,6 +184,16 @@ sha256_final(SHA256_CTX *ctx, nsword8 ha
         hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
         hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
         hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
+#else
+        hash[i]      = (ctx->state[1] >> (i * 8)) & 0x000000ff;
+        hash[i + 4]  = (ctx->state[0] >> (i * 8)) & 0x000000ff;
+        hash[i + 8]  = (ctx->state[3] >> (i * 8)) & 0x000000ff;
+        hash[i + 12] = (ctx->state[2] >> (i * 8)) & 0x000000ff;
+        hash[i + 16] = (ctx->state[5] >> (i * 8)) & 0x000000ff;
+        hash[i + 20] = (ctx->state[4] >> (i * 8)) & 0x000000ff;
+        hash[i + 24] = (ctx->state[7] >> (i * 8)) & 0x000000ff;
+        hash[i + 28] = (ctx->state[6] >> (i * 8)) & 0x000000ff;
+#endif
     }
 }

-- 
Jerry James
http://www.jamezone.org/