| /*- |
| * Copyright (c) 2017 Steven G. Kargl |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice unmodified, this list of conditions, and the following |
| * disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
| * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
| * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
| * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
| * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| /** |
| * cospi(x) computes cos(pi*x) without multiplication by pi (almost). First, |
| * note that cospi(-x) = cospi(x), so the algorithm considers only |x|. The |
| * method used depends on the magnitude of x. |
| * |
| * 1. For small |x|, cospi(x) = 1 with FE_INEXACT raised where a sloppy |
| * threshold is used. The threshold is |x| < 0x1pN with N = -(P/2+M). |
| * P is the precision of the floating-point type and M = 2 to 4. |
| * |
| * 2. For |x| < 1, argument reduction is not required and sinpi(x) is |
| * computed by calling a kernel that leverages the kernels for sin(x) |
| * ans cos(x). See k_sinpi.c and k_cospi.c for details. |
| * |
| * 3. For 1 <= |x| < 0x1p(P-1), argument reduction is required where |
| * |x| = j0 + r with j0 an integer and the remainder r satisfies |
| * 0 <= r < 1. With the given domain, a simplified inline floor(x) |
| * is used. Also, note the following identity |
| * |
| * cospi(x) = cos(pi*(j0+r)) |
| * = cos(pi*j0) * cos(pi*r) - sin(pi*j0) * sin(pi*r) |
| * = cos(pi*j0) * cos(pi*r) |
| * = +-cospi(r) |
| * |
| * If j0 is even, then cos(pi*j0) = 1. If j0 is odd, then cos(pi*j0) = -1. |
| * cospi(r) is then computed via an appropriate kernel. |
| * |
| * 4. For |x| >= 0x1p(P-1), |x| is integral and cospi(x) = 1. |
| * |
| * 5. Special cases: |
| * |
| * cospi(+-0) = 1. |
| * cospi(n.5) = 0 for n an integer. |
| * cospi(+-inf) = nan. Raises the "invalid" floating-point exception. |
| * cospi(nan) = nan. Raises the "invalid" floating-point exception. |
| */ |
| |
| #include <float.h> |
| #include "math.h" |
| #include "math_private.h" |
| |
| static const double |
| pi_hi = 3.1415926814079285e+00, /* 0x400921fb 0x58000000 */ |
| pi_lo =-2.7818135228334233e-08; /* 0xbe5dde97 0x3dcb3b3a */ |
| |
| #include "k_cospi.h" |
| #include "k_sinpi.h" |
| |
| volatile static const double vzero = 0; |
| |
| double |
| cospi(double x) |
| { |
| double ax, c; |
| uint32_t hx, ix, j0, lx; |
| |
| EXTRACT_WORDS(hx, lx, x); |
| ix = hx & 0x7fffffff; |
| INSERT_WORDS(ax, ix, lx); |
| |
| if (ix < 0x3ff00000) { /* |x| < 1 */ |
| if (ix < 0x3fd00000) { /* |x| < 0.25 */ |
| if (ix < 0x3e200000) { /* |x| < 0x1p-29 */ |
| if ((int)ax == 0) |
| return (1); |
| } |
| return (__kernel_cospi(ax)); |
| } |
| |
| if (ix < 0x3fe00000) /* |x| < 0.5 */ |
| c = __kernel_sinpi(0.5 - ax); |
| else if (ix < 0x3fe80000){ /* |x| < 0.75 */ |
| if (ax == 0.5) |
| return (0); |
| c = -__kernel_sinpi(ax - 0.5); |
| } else |
| c = -__kernel_cospi(1 - ax); |
| return (c); |
| } |
| |
| if (ix < 0x43300000) { /* 1 <= |x| < 0x1p52 */ |
| /* Determine integer part of ax. */ |
| j0 = ((ix >> 20) & 0x7ff) - 0x3ff; |
| if (j0 < 20) { |
| ix &= ~(0x000fffff >> j0); |
| lx = 0; |
| } else { |
| lx &= ~((uint32_t)0xffffffff >> (j0 - 20)); |
| } |
| INSERT_WORDS(x, ix, lx); |
| |
| ax -= x; |
| EXTRACT_WORDS(ix, lx, ax); |
| |
| |
| if (ix < 0x3fe00000) { /* |x| < 0.5 */ |
| if (ix < 0x3fd00000) /* |x| < 0.25 */ |
| c = ix == 0 ? 1 : __kernel_cospi(ax); |
| else |
| c = __kernel_sinpi(0.5 - ax); |
| } else { |
| if (ix < 0x3fe80000) { /* |x| < 0.75 */ |
| if (ax == 0.5) |
| return (0); |
| c = -__kernel_sinpi(ax - 0.5); |
| } else |
| c = -__kernel_cospi(1 - ax); |
| } |
| |
| if (j0 > 30) |
| x -= 0x1p30; |
| j0 = (uint32_t)x; |
| return (j0 & 1 ? -c : c); |
| } |
| |
| if (ix >= 0x7f800000) |
| return (vzero / vzero); |
| |
| /* |
| * |x| >= 0x1p52 is always an even integer, so return 1. |
| */ |
| return (1); |
| } |
| |
| #if LDBL_MANT_DIG == 53 |
| __weak_reference(cospi, cospil); |
| #endif |