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authordrochner <drochner@NetBSD.org>2006-03-22 21:06:03 +0000
committerdrochner <drochner@NetBSD.org>2006-03-22 21:06:03 +0000
commit7a2af2aba0675e60300e041f8514eb775a203229 (patch)
treef50f6fbde7e7e191372c66d1f95fb3b7043329f9 /lib/libc/stdlib
parente89a43e9fd4f84bfb3004474083438814d0f8674 (diff)
Rewrite erand48() to put the random bits into the mantissa by simple
bitshifts instead of calling ldexp() three times. (for ieee doubles only -- vax can't use it, so the old version needs to stay around) This removes the dependency on ldexp() which also didn't participate in the usual __RENAME game, thus lead to confusion. In addition, this version is almost 3 times as fast for me.
Diffstat (limited to 'lib/libc/stdlib')
-rw-r--r--lib/libc/stdlib/erand48_ieee754.c47
1 files changed, 47 insertions, 0 deletions
diff --git a/lib/libc/stdlib/erand48_ieee754.c b/lib/libc/stdlib/erand48_ieee754.c
new file mode 100644
index 00000000000..f3874502875
--- /dev/null
+++ b/lib/libc/stdlib/erand48_ieee754.c
@@ -0,0 +1,47 @@
+/* $NetBSD: erand48_ieee754.c,v 1.1 2006/03/22 21:06:03 drochner Exp $ */
+
+/*
+ * Copyright (c) 1993 Martin Birgmeier
+ * All rights reserved.
+ *
+ * You may redistribute unmodified or modified versions of this source
+ * code provided that the above copyright notice and this and the
+ * following conditions are retained.
+ *
+ * This software is provided ``as is'', and comes with no warranties
+ * of any kind. I shall in no event be liable for anything that happens
+ * to anyone/anything when using this software.
+ */
+
+#include <sys/cdefs.h>
+#if defined(LIBC_SCCS) && !defined(lint)
+__RCSID("$NetBSD: erand48_ieee754.c,v 1.1 2006/03/22 21:06:03 drochner Exp $");
+#endif /* LIBC_SCCS and not lint */
+
+#include "namespace.h"
+
+#include <assert.h>
+#include <machine/ieee.h>
+
+#include "rand48.h"
+
+#ifdef __weak_alias
+__weak_alias(erand48,_erand48)
+#endif
+
+double
+erand48(unsigned short xseed[3])
+{
+ union ieee_double_u u;
+
+ _DIAGASSERT(xseed != NULL);
+
+ __dorand48(xseed);
+ u.dblu_dbl.dbl_sign = 0;
+ u.dblu_dbl.dbl_exp = DBL_EXP_BIAS; /* so we get [1,2) */
+ u.dblu_dbl.dbl_frach = ((unsigned int)xseed[0] << 4)
+ | ((unsigned int)xseed[1] >> 12);
+ u.dblu_dbl.dbl_fracl = (((unsigned int)xseed[1] & 0x0fff) << 20)
+ | ((unsigned int)xseed[2] << 4);
+ return (u.dblu_d - 1);
+}