xref: /minix/lib/libm/src/e_rem_pio2f.c (revision 2fe8fb19)
1 /* e_rem_pio2f.c -- float version of e_rem_pio2.c
2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3  */
4 
5 /*
6  * ====================================================
7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8  *
9  * Developed at SunPro, a Sun Microsystems, Inc. business.
10  * Permission to use, copy, modify, and distribute this
11  * software is freely granted, provided that this notice
12  * is preserved.
13  * ====================================================
14  */
15 
16 #include <sys/cdefs.h>
17 #if defined(LIBM_SCCS) && !defined(lint)
18 __RCSID("$NetBSD: e_rem_pio2f.c,v 1.9 2009/01/19 06:00:30 lukem Exp $");
19 #endif
20 
21 /* __ieee754_rem_pio2f(x,y)
22  *
23  * return the remainder of x rem pi/2 in y[0]+y[1]
24  * use __kernel_rem_pio2f()
25  */
26 
27 #include "math.h"
28 #include "math_private.h"
29 
30 /*
31  * Table of constants for 2/pi, 396 Hex digits (476 decimal) of 2/pi
32  */
33 static const int32_t two_over_pi[] = {
34 0xA2, 0xF9, 0x83, 0x6E, 0x4E, 0x44, 0x15, 0x29, 0xFC,
35 0x27, 0x57, 0xD1, 0xF5, 0x34, 0xDD, 0xC0, 0xDB, 0x62,
36 0x95, 0x99, 0x3C, 0x43, 0x90, 0x41, 0xFE, 0x51, 0x63,
37 0xAB, 0xDE, 0xBB, 0xC5, 0x61, 0xB7, 0x24, 0x6E, 0x3A,
38 0x42, 0x4D, 0xD2, 0xE0, 0x06, 0x49, 0x2E, 0xEA, 0x09,
39 0xD1, 0x92, 0x1C, 0xFE, 0x1D, 0xEB, 0x1C, 0xB1, 0x29,
40 0xA7, 0x3E, 0xE8, 0x82, 0x35, 0xF5, 0x2E, 0xBB, 0x44,
41 0x84, 0xE9, 0x9C, 0x70, 0x26, 0xB4, 0x5F, 0x7E, 0x41,
42 0x39, 0x91, 0xD6, 0x39, 0x83, 0x53, 0x39, 0xF4, 0x9C,
43 0x84, 0x5F, 0x8B, 0xBD, 0xF9, 0x28, 0x3B, 0x1F, 0xF8,
44 0x97, 0xFF, 0xDE, 0x05, 0x98, 0x0F, 0xEF, 0x2F, 0x11,
45 0x8B, 0x5A, 0x0A, 0x6D, 0x1F, 0x6D, 0x36, 0x7E, 0xCF,
46 0x27, 0xCB, 0x09, 0xB7, 0x4F, 0x46, 0x3F, 0x66, 0x9E,
47 0x5F, 0xEA, 0x2D, 0x75, 0x27, 0xBA, 0xC7, 0xEB, 0xE5,
48 0xF1, 0x7B, 0x3D, 0x07, 0x39, 0xF7, 0x8A, 0x52, 0x92,
49 0xEA, 0x6B, 0xFB, 0x5F, 0xB1, 0x1F, 0x8D, 0x5D, 0x08,
50 0x56, 0x03, 0x30, 0x46, 0xFC, 0x7B, 0x6B, 0xAB, 0xF0,
51 0xCF, 0xBC, 0x20, 0x9A, 0xF4, 0x36, 0x1D, 0xA9, 0xE3,
52 0x91, 0x61, 0x5E, 0xE6, 0x1B, 0x08, 0x65, 0x99, 0x85,
53 0x5F, 0x14, 0xA0, 0x68, 0x40, 0x8D, 0xFF, 0xD8, 0x80,
54 0x4D, 0x73, 0x27, 0x31, 0x06, 0x06, 0x15, 0x56, 0xCA,
55 0x73, 0xA8, 0xC9, 0x60, 0xE2, 0x7B, 0xC0, 0x8C, 0x6B,
56 };
57 
58 /* This array is like the one in e_rem_pio2.c, but the numbers are
59    single precision and the last 8 bits are forced to 0.  */
60 static const int32_t npio2_hw[] = {
61 0x3fc90f00, 0x40490f00, 0x4096cb00, 0x40c90f00, 0x40fb5300, 0x4116cb00,
62 0x412fed00, 0x41490f00, 0x41623100, 0x417b5300, 0x418a3a00, 0x4196cb00,
63 0x41a35c00, 0x41afed00, 0x41bc7e00, 0x41c90f00, 0x41d5a000, 0x41e23100,
64 0x41eec200, 0x41fb5300, 0x4203f200, 0x420a3a00, 0x42108300, 0x4216cb00,
65 0x421d1400, 0x42235c00, 0x4229a500, 0x422fed00, 0x42363600, 0x423c7e00,
66 0x4242c700, 0x42490f00
67 };
68 
69 /*
70  * invpio2:  24 bits of 2/pi
71  * pio2_1:   first  17 bit of pi/2
72  * pio2_1t:  pi/2 - pio2_1
73  * pio2_2:   second 17 bit of pi/2
74  * pio2_2t:  pi/2 - (pio2_1+pio2_2)
75  * pio2_3:   third  17 bit of pi/2
76  * pio2_3t:  pi/2 - (pio2_1+pio2_2+pio2_3)
77  */
78 
79 static const float
80 zero =  0.0000000000e+00, /* 0x00000000 */
81 half =  5.0000000000e-01, /* 0x3f000000 */
82 two8 =  2.5600000000e+02, /* 0x43800000 */
83 invpio2 =  6.3661980629e-01, /* 0x3f22f984 */
84 pio2_1  =  1.5707855225e+00, /* 0x3fc90f80 */
85 pio2_1t =  1.0804334124e-05, /* 0x37354443 */
86 pio2_2  =  1.0804273188e-05, /* 0x37354400 */
87 pio2_2t =  6.0770999344e-11, /* 0x2e85a308 */
88 pio2_3  =  6.0770943833e-11, /* 0x2e85a300 */
89 pio2_3t =  6.1232342629e-17; /* 0x248d3132 */
90 
91 int32_t
__ieee754_rem_pio2f(float x,float * y)92 __ieee754_rem_pio2f(float x, float *y)
93 {
94 	float z,w,t,r,fn;
95 	float tx[3];
96 	int32_t e0,i,j,nx,n,ix,hx;
97 
98 	GET_FLOAT_WORD(hx,x);
99 	ix = hx&0x7fffffff;
100 	if(ix<=0x3f490fd8)   /* |x| ~<= pi/4 , no need for reduction */
101 	    {y[0] = x; y[1] = 0; return 0;}
102 	if(ix<0x4016cbe4) {  /* |x| < 3pi/4, special case with n=+-1 */
103 	    if(hx>0) {
104 		z = x - pio2_1;
105 		if((ix&0xfffffff0)!=0x3fc90fd0) { /* 24+24 bit pi OK */
106 		    y[0] = z - pio2_1t;
107 		    y[1] = (z-y[0])-pio2_1t;
108 		} else {		/* near pi/2, use 24+24+24 bit pi */
109 		    z -= pio2_2;
110 		    y[0] = z - pio2_2t;
111 		    y[1] = (z-y[0])-pio2_2t;
112 		}
113 		return 1;
114 	    } else {	/* negative x */
115 		z = x + pio2_1;
116 		if((ix&0xfffffff0)!=0x3fc90fd0) { /* 24+24 bit pi OK */
117 		    y[0] = z + pio2_1t;
118 		    y[1] = (z-y[0])+pio2_1t;
119 		} else {		/* near pi/2, use 24+24+24 bit pi */
120 		    z += pio2_2;
121 		    y[0] = z + pio2_2t;
122 		    y[1] = (z-y[0])+pio2_2t;
123 		}
124 		return -1;
125 	    }
126 	}
127 	if(ix<=0x43490f80) { /* |x| ~<= 2^7*(pi/2), medium size */
128 	    t  = fabsf(x);
129 	    n  = (int32_t) (t*invpio2+half);
130 	    fn = (float)n;
131 	    r  = t-fn*pio2_1;
132 	    w  = fn*pio2_1t;	/* 1st round good to 40 bit */
133 	    if(n<32&&(int32_t)(ix&0xffffff00)!=npio2_hw[n-1]) {
134 		y[0] = r-w;	/* quick check no cancellation */
135 	    } else {
136 	        u_int32_t high;
137 	        j  = ix>>23;
138 	        y[0] = r-w;
139 		GET_FLOAT_WORD(high,y[0]);
140 	        i = j-((high>>23)&0xff);
141 	        if(i>8) {  /* 2nd iteration needed, good to 57 */
142 		    t  = r;
143 		    w  = fn*pio2_2;
144 		    r  = t-w;
145 		    w  = fn*pio2_2t-((t-r)-w);
146 		    y[0] = r-w;
147 		    GET_FLOAT_WORD(high,y[0]);
148 		    i = j-((high>>23)&0xff);
149 		    if(i>25)  {	/* 3rd iteration need, 74 bits acc */
150 		    	t  = r;	/* will cover all possible cases */
151 		    	w  = fn*pio2_3;
152 		    	r  = t-w;
153 		    	w  = fn*pio2_3t-((t-r)-w);
154 		    	y[0] = r-w;
155 		    }
156 		}
157 	    }
158 	    y[1] = (r-y[0])-w;
159 	    if(hx<0) 	{y[0] = -y[0]; y[1] = -y[1]; return -n;}
160 	    else	 return n;
161 	}
162     /*
163      * all other (large) arguments
164      */
165 	if(ix>=0x7f800000) {		/* x is inf or NaN */
166 	    y[0]=y[1]=x-x; return 0;
167 	}
168     /* set z = scalbn(|x|,ilogb(x)-7) */
169 	e0 	= (ix>>23)-134;		/* e0 = ilogb(z)-7; */
170 	SET_FLOAT_WORD(z, ix - ((int32_t)(e0<<23)));
171 	for(i=0;i<2;i++) {
172 		tx[i] = (float)((int32_t)(z));
173 		z     = (z-tx[i])*two8;
174 	}
175 	tx[2] = z;
176 	nx = 3;
177 	while(tx[nx-1]==zero) nx--;	/* skip zero term */
178 	n  =  __kernel_rem_pio2f(tx,y,e0,nx,2,two_over_pi);
179 	if(hx<0) {y[0] = -y[0]; y[1] = -y[1]; return -n;}
180 	return n;
181 }
182