summaryrefslogtreecommitdiff
path: root/src/math/__cosl.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/math/__cosl.c')
-rw-r--r--src/math/__cosl.c76
1 files changed, 76 insertions, 0 deletions
diff --git a/src/math/__cosl.c b/src/math/__cosl.c
new file mode 100644
index 00000000..9ea51ecf
--- /dev/null
+++ b/src/math/__cosl.c
@@ -0,0 +1,76 @@
+/* origin: FreeBSD /usr/src/lib/msun/ld80/k_cosl.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ * Copyright (c) 2008 Steven G. Kargl, David Schultz, Bruce D. Evans.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+/*
+ * ld80 version of __cos.c. See __cos.c for most comments.
+ */
+/*
+ * Domain [-0.7854, 0.7854], range ~[-2.43e-23, 2.425e-23]:
+ * |cos(x) - c(x)| < 2**-75.1
+ *
+ * The coefficients of c(x) were generated by a pari-gp script using
+ * a Remez algorithm that searches for the best higher coefficients
+ * after rounding leading coefficients to a specified precision.
+ *
+ * Simpler methods like Chebyshev or basic Remez barely suffice for
+ * cos() in 64-bit precision, because we want the coefficient of x^2
+ * to be precisely -0.5 so that multiplying by it is exact, and plain
+ * rounding of the coefficients of a good polynomial approximation only
+ * gives this up to about 64-bit precision. Plain rounding also gives
+ * a mediocre approximation for the coefficient of x^4, but a rounding
+ * error of 0.5 ulps for this coefficient would only contribute ~0.01
+ * ulps to the final error, so this is unimportant. Rounding errors in
+ * higher coefficients are even less important.
+ *
+ * In fact, coefficients above the x^4 one only need to have 53-bit
+ * precision, and this is more efficient. We get this optimization
+ * almost for free from the complications needed to search for the best
+ * higher coefficients.
+ */
+static const double one = 1.0;
+
+// FIXME
+/* Long double constants are slow on these arches, and broken on i386. */
+static const volatile double
+C1hi = 0.041666666666666664, /* 0x15555555555555.0p-57 */
+C1lo = 2.2598839032744733e-18; /* 0x14d80000000000.0p-111 */
+#define C1 ((long double)C1hi + C1lo)
+
+#if 0
+static const long double
+C1 = 0.0416666666666666666136L; /* 0xaaaaaaaaaaaaaa9b.0p-68 */
+#endif
+
+static const double
+C2 = -0.0013888888888888874, /* -0x16c16c16c16c10.0p-62 */
+C3 = 0.000024801587301571716, /* 0x1a01a01a018e22.0p-68 */
+C4 = -0.00000027557319215507120, /* -0x127e4fb7602f22.0p-74 */
+C5 = 0.0000000020876754400407278, /* 0x11eed8caaeccf1.0p-81 */
+C6 = -1.1470297442401303e-11, /* -0x19393412bd1529.0p-89 */
+C7 = 4.7383039476436467e-14; /* 0x1aac9d9af5c43e.0p-97 */
+
+long double __cosl(long double x, long double y)
+{
+ long double hz,z,r,w;
+
+ z = x*x;
+ r = z*(C1+z*(C2+z*(C3+z*(C4+z*(C5+z*(C6+z*C7))))));
+ hz = 0.5*z;
+ w = one-hz;
+ return w + (((one-w)-hz) + (z*r-x*y));
+}
+#endif