X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/119bdfc4c80e313417047de10700e6b8c3955d0d..25f3ce6a509ff9e3a354303023cb2028e9f83b95:/base/dispatch-x86ish.S

diff --git a/base/dispatch-x86ish.S b/base/dispatch-x86ish.S
index 2c267b62..3e2d4c83 100644
--- a/base/dispatch-x86ish.S
+++ b/base/dispatch-x86ish.S
@@ -153,4 +153,47 @@ FUNC(dispatch_x86ish_xmmregisters_p)
 	ret
 ENDFUNC
 
+///--------------------------------------------------------------------------
+/// Checking `rdrand'.
+
+FUNC(dispatch_x86ish_rdrand)
+	// Enter with one argument: a pointer X_OUT to a 32-bit word.  Try to
+	// generate a random word using `rdrand'.  If successful, set *X_OUT
+	// to the generated word, and return zero; otherwise, return -1.
+
+#if CPUFAM_X86
+#  define X_OUT edx
+#  define COUNT ecx
+	mov	X_OUT, [SP + 4]
+#endif
+#if CPUFAM_AMD64 && ABI_SYSV
+#  define X_OUT rdi
+#  define COUNT ecx
+#endif
+#if CPUFAM_AMD64 && ABI_WIN
+#  define X_OUT rcx
+#  define COUNT edx
+#endif
+  endprologue
+
+	mov	COUNT, 16		// fairly persistent
+0:	rdrand	eax
+	jc	9f
+	dec	COUNT
+	jnz	0b
+
+	// Failed to come up with a random value.
+	mov	eax, -1
+	ret
+
+	// Success.
+9:	mov	[X_OUT], eax
+	xor	eax, eax
+	ret
+
+#undef X_OUT
+#undef COUNT
+
+ENDFUNC
+
 ///----- That's all, folks --------------------------------------------------