Optimize scalbln

1 files changed, 60 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c
new file mode 100644
index 0000000000..d6b97b5483
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c
@@ -0,0 +1,60 @@
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+/*
+ * scalbn (double x, int n)
+ * scalbn(x,n) returns x* 2**n  computed by  exponent
+ * manipulation rather than by actually performing an
+ * exponentiation or a multiplication.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+static const double
+two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
+huge   = 1.0e+300,
+tiny   = 1.0e-300;
+
+double
+__scalbln (double x, long int n)
+{
+	int64_t ix;
+	int64_t k;
+	EXTRACT_WORDS64(ix,x);
+	k = (ix >> 52) & 0x7ff;			/* extract exponent */
+	if (__builtin_expect(k==0, 0)) {	/* 0 or subnormal x */
+	    if ((ix & UINT64_C(0xfffffffffffff))==0) return x; /* +-0 */
+	    x *= two54;
+	    EXTRACT_WORDS64(ix,x);
+	    k = ((ix >> 52) & 0x7ff) - 54;
+	    }
+	if (__builtin_expect(k==0x7ff, 0)) return x+x;	/* NaN or Inf */
+	k = k+n;
+	if (__builtin_expect(n> 50000 || k >  0x7fe, 0))
+	  return huge*__copysign(huge,x); /* overflow  */
+	if (__builtin_expect(n< -50000, 0))
+	  return tiny*__copysign(tiny,x); /*underflow*/
+	if (__builtin_expect(k > 0, 1))		/* normal result */
+	    {INSERT_WORDS64(x,(ix&UINT64_C(0x800fffffffffffff))|(k<<52));
+	      return x;}
+	if (k <= -54)
+	  return tiny*__copysign(tiny,x);	/*underflow*/
+	k += 54;				/* subnormal result */
+	INSERT_WORDS64(x,(ix&INT64_C(0x800fffffffffffff))|(k<<52));
+	return x*twom54;
+}
+weak_alias (__scalbln, scalbln)
+#ifdef NO_LONG_DOUBLE
+strong_alias (__scalbln, __scalblnl)
+weak_alias (__scalbln, scalblnl)
+#endif