first commit of the new libm!

[musl] / src / math / scalbn.c

diff --git a/src/math/scalbn.c b/src/math/scalbn.c
new file mode 100644 (file)
index 0000000..b51551b
--- /dev/null
+++ b/src/math/scalbn.c
@@ -0,0 +1,62 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbn.c */
+/*
+ * ====================================================
+ * 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 "libm.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 scalbn(double x, int n)
+{
+// FIXME: k+n check depends on signed int overflow.. use unsigned hx
+// TODO: when long != int:
+//       scalbln(x,long n) { if(n>9999)n=9999; else if(n<-9999)n=-9999; return scalbn(x,n); }
+// TODO: n < -50000 ...
+       int32_t k,hx,lx;
+
+       EXTRACT_WORDS(hx, lx, x);
+       k = (hx&0x7ff00000)>>20;                /* extract exponent */
+       if (k == 0) {                           /* 0 or subnormal x */
+               if ((lx|(hx&0x7fffffff)) == 0)  /* +-0 */
+                       return x;
+               x *= two54;
+               GET_HIGH_WORD(hx, x);
+               k = ((hx&0x7ff00000)>>20) - 54;
+               if (n < -50000)
+                       return tiny*x;          /*underflow*/
+       }
+       if (k == 0x7ff)                         /* NaN or Inf */
+               return x + x;
+       k = k + n;
+       if (k > 0x7fe)
+               return huge*copysign(huge, x);  /* overflow  */
+       if (k > 0) {                            /* normal result */
+               SET_HIGH_WORD(x, (hx&0x800fffff)|(k<<20));
+               return x;
+       }
+       if (k <= -54)
+               if (n > 50000)      /* in case integer overflow in n+k */
+                       return huge*copysign(huge, x);  /*overflow*/
+               return tiny*copysign(tiny, x);  /*underflow*/
+       k += 54;                                /* subnormal result */
+       SET_HIGH_WORD(x, (hx&0x800fffff)|(k<<20));
+       return x*twom54;
+}