Patch to FLAC to allow it to detect Altivec on non-Darwin operating systems.

By John Steele Scott <toojays@toojays.net>, 17 October 2004.

Regular FLAC 1.1.1 only turns on the Altivec optimisations on Darwin-based
OSs. This patch allows it to check for Altivec on other operating systems. It
works by attempting to execute a Altivec instruction, and catching the
illegal-instruction signal if it fails. This approach and code was taken from
MPlayer, although I believe it is the same approach as suggested by Apple for
cross-platform code.

--- flac-1.1.1/src/libFLAC/cpu.c	2004-07-27 10:13:00.000000000 +0930
+++ flac-1.1.1-linux/src/libFLAC/cpu.c	2004-10-17 18:11:54.717777416 +0930
@@ -41,6 +41,23 @@
 #if !defined FLAC__NO_ASM
 #if defined __APPLE__ && defined __MACH__
 #include <sys/sysctl.h>
+#else /* __APPLE__ && __MACH__ */
+#include <signal.h>
+#include <setjmp.h>
+
+static sigjmp_buf jmpbuf;
+static volatile sig_atomic_t canjump = 0;
+
+static void sigill_handler (int sig)
+{
+    if (!canjump) {
+        signal (sig, SIG_DFL);
+        raise (sig);
+    }
+    
+    canjump = 0;
+    siglongjmp (jmpbuf, 1);
+}
 #endif /* __APPLE__ && __MACH__ */
 #endif /* FLAC__NO_ASM */
 #endif /* FLAC__CPU_PPC */
@@ -101,8 +118,25 @@
 		info->data.ppc.altivec = error==0 ? result!=0 : 0;
 	}
 #else /* __APPLE__ && __MACH__ */
-	/* don't know of any other thread-safe way to check */
-	info->data.ppc.altivec = 0;
+        /* no Darwin, do it the brute-force way */
+        /* borrowed from mplayer, which got it from the libmpeg2 library */
+        {
+		info->data.ppc.altivec = 0;
+		signal (SIGILL, sigill_handler);
+		if (sigsetjmp (jmpbuf, 1)) {
+			signal (SIGILL, SIG_DFL);
+		} else {
+			canjump = 1;
+			
+			asm volatile ("mtspr 256, %0\n\t"
+				      "vand %%v0, %%v0, %%v0"
+				      :
+				      : "r" (-1));
+            
+			signal (SIGILL, SIG_DFL);
+			info->data.ppc.altivec = 1;
+		}
+	}
 #endif /* __APPLE__ && __MACH__ */
 #else /* FLAC__USE_ALTIVEC */
 	info->data.ppc.altivec = 0;