Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | /*---------------------------------------------------------------------------+ |
2 | | poly_l2.c | | |
3 | | | | |
4 | | Compute the base 2 log of a FPU_REG, using a polynomial approximation. | | |
5 | | | | |
6 | | Copyright (C) 1992,1993,1994,1997 | | |
7 | | W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia | | |
8 | | E-mail billm@suburbia.net | | |
9 | | | | |
10 | | | | |
11 | +---------------------------------------------------------------------------*/ | |
12 | ||
1da177e4 LT |
13 | #include "exception.h" |
14 | #include "reg_constant.h" | |
15 | #include "fpu_emu.h" | |
16 | #include "fpu_system.h" | |
17 | #include "control_w.h" | |
18 | #include "poly.h" | |
19 | ||
1da177e4 | 20 | static void log2_kernel(FPU_REG const *arg, u_char argsign, |
3d0d14f9 | 21 | Xsig * accum_result, long int *expon); |
1da177e4 LT |
22 | |
23 | /*--- poly_l2() -------------------------------------------------------------+ | |
24 | | Base 2 logarithm by a polynomial approximation. | | |
25 | +---------------------------------------------------------------------------*/ | |
e8d591dc | 26 | void poly_l2(FPU_REG *st0_ptr, FPU_REG *st1_ptr, u_char st1_sign) |
1da177e4 | 27 | { |
3d0d14f9 IM |
28 | long int exponent, expon, expon_expon; |
29 | Xsig accumulator, expon_accum, yaccum; | |
30 | u_char sign, argsign; | |
31 | FPU_REG x; | |
32 | int tag; | |
33 | ||
34 | exponent = exponent16(st0_ptr); | |
35 | ||
36 | /* From st0_ptr, make a number > sqrt(2)/2 and < sqrt(2) */ | |
37 | if (st0_ptr->sigh > (unsigned)0xb504f334) { | |
38 | /* Treat as sqrt(2)/2 < st0_ptr < 1 */ | |
39 | significand(&x) = -significand(st0_ptr); | |
40 | setexponent16(&x, -1); | |
41 | exponent++; | |
42 | argsign = SIGN_NEG; | |
43 | } else { | |
44 | /* Treat as 1 <= st0_ptr < sqrt(2) */ | |
45 | x.sigh = st0_ptr->sigh - 0x80000000; | |
46 | x.sigl = st0_ptr->sigl; | |
47 | setexponent16(&x, 0); | |
48 | argsign = SIGN_POS; | |
49 | } | |
50 | tag = FPU_normalize_nuo(&x); | |
1da177e4 | 51 | |
3d0d14f9 IM |
52 | if (tag == TAG_Zero) { |
53 | expon = 0; | |
54 | accumulator.msw = accumulator.midw = accumulator.lsw = 0; | |
55 | } else { | |
56 | log2_kernel(&x, argsign, &accumulator, &expon); | |
57 | } | |
58 | ||
59 | if (exponent < 0) { | |
60 | sign = SIGN_NEG; | |
61 | exponent = -exponent; | |
62 | } else | |
63 | sign = SIGN_POS; | |
64 | expon_accum.msw = exponent; | |
65 | expon_accum.midw = expon_accum.lsw = 0; | |
66 | if (exponent) { | |
67 | expon_expon = 31 + norm_Xsig(&expon_accum); | |
68 | shr_Xsig(&accumulator, expon_expon - expon); | |
69 | ||
70 | if (sign ^ argsign) | |
71 | negate_Xsig(&accumulator); | |
72 | add_Xsig_Xsig(&accumulator, &expon_accum); | |
73 | } else { | |
74 | expon_expon = expon; | |
75 | sign = argsign; | |
76 | } | |
77 | ||
78 | yaccum.lsw = 0; | |
79 | XSIG_LL(yaccum) = significand(st1_ptr); | |
80 | mul_Xsig_Xsig(&accumulator, &yaccum); | |
81 | ||
82 | expon_expon += round_Xsig(&accumulator); | |
83 | ||
84 | if (accumulator.msw == 0) { | |
85 | FPU_copy_to_reg1(&CONST_Z, TAG_Zero); | |
86 | return; | |
87 | } | |
88 | ||
89 | significand(st1_ptr) = XSIG_LL(accumulator); | |
90 | setexponent16(st1_ptr, expon_expon + exponent16(st1_ptr) + 1); | |
1da177e4 | 91 | |
3d0d14f9 IM |
92 | tag = FPU_round(st1_ptr, 1, 0, FULL_PRECISION, sign ^ st1_sign); |
93 | FPU_settagi(1, tag); | |
94 | ||
95 | set_precision_flag_up(); /* 80486 appears to always do this */ | |
96 | ||
97 | return; | |
98 | ||
99 | } | |
1da177e4 LT |
100 | |
101 | /*--- poly_l2p1() -----------------------------------------------------------+ | |
102 | | Base 2 logarithm by a polynomial approximation. | | |
103 | | log2(x+1) | | |
104 | +---------------------------------------------------------------------------*/ | |
3d0d14f9 IM |
105 | int poly_l2p1(u_char sign0, u_char sign1, |
106 | FPU_REG * st0_ptr, FPU_REG * st1_ptr, FPU_REG * dest) | |
1da177e4 | 107 | { |
3d0d14f9 IM |
108 | u_char tag; |
109 | long int exponent; | |
110 | Xsig accumulator, yaccum; | |
1da177e4 | 111 | |
3d0d14f9 IM |
112 | if (exponent16(st0_ptr) < 0) { |
113 | log2_kernel(st0_ptr, sign0, &accumulator, &exponent); | |
1da177e4 | 114 | |
3d0d14f9 IM |
115 | yaccum.lsw = 0; |
116 | XSIG_LL(yaccum) = significand(st1_ptr); | |
117 | mul_Xsig_Xsig(&accumulator, &yaccum); | |
1da177e4 | 118 | |
3d0d14f9 | 119 | exponent += round_Xsig(&accumulator); |
1da177e4 | 120 | |
3d0d14f9 IM |
121 | exponent += exponent16(st1_ptr) + 1; |
122 | if (exponent < EXP_WAY_UNDER) | |
123 | exponent = EXP_WAY_UNDER; | |
1da177e4 | 124 | |
3d0d14f9 IM |
125 | significand(dest) = XSIG_LL(accumulator); |
126 | setexponent16(dest, exponent); | |
1da177e4 | 127 | |
3d0d14f9 IM |
128 | tag = FPU_round(dest, 1, 0, FULL_PRECISION, sign0 ^ sign1); |
129 | FPU_settagi(1, tag); | |
1da177e4 | 130 | |
3d0d14f9 IM |
131 | if (tag == TAG_Valid) |
132 | set_precision_flag_up(); /* 80486 appears to always do this */ | |
133 | } else { | |
134 | /* The magnitude of st0_ptr is far too large. */ | |
1da177e4 | 135 | |
3d0d14f9 IM |
136 | if (sign0 != SIGN_POS) { |
137 | /* Trying to get the log of a negative number. */ | |
138 | #ifdef PECULIAR_486 /* Stupid 80486 doesn't worry about log(negative). */ | |
139 | changesign(st1_ptr); | |
1da177e4 | 140 | #else |
3d0d14f9 IM |
141 | if (arith_invalid(1) < 0) |
142 | return 1; | |
1da177e4 | 143 | #endif /* PECULIAR_486 */ |
3d0d14f9 | 144 | } |
1da177e4 | 145 | |
3d0d14f9 IM |
146 | /* 80486 appears to do this */ |
147 | if (sign0 == SIGN_NEG) | |
148 | set_precision_flag_down(); | |
149 | else | |
150 | set_precision_flag_up(); | |
151 | } | |
1da177e4 | 152 | |
3d0d14f9 IM |
153 | if (exponent(dest) <= EXP_UNDER) |
154 | EXCEPTION(EX_Underflow); | |
1da177e4 | 155 | |
3d0d14f9 | 156 | return 0; |
1da177e4 LT |
157 | |
158 | } | |
159 | ||
1da177e4 LT |
160 | #undef HIPOWER |
161 | #define HIPOWER 10 | |
3d0d14f9 IM |
162 | static const unsigned long long logterms[HIPOWER] = { |
163 | 0x2a8eca5705fc2ef0LL, | |
164 | 0xf6384ee1d01febceLL, | |
165 | 0x093bb62877cdf642LL, | |
166 | 0x006985d8a9ec439bLL, | |
167 | 0x0005212c4f55a9c8LL, | |
168 | 0x00004326a16927f0LL, | |
169 | 0x0000038d1d80a0e7LL, | |
170 | 0x0000003141cc80c6LL, | |
171 | 0x00000002b1668c9fLL, | |
172 | 0x000000002c7a46aaLL | |
1da177e4 LT |
173 | }; |
174 | ||
175 | static const unsigned long leadterm = 0xb8000000; | |
176 | ||
1da177e4 LT |
177 | /*--- log2_kernel() ---------------------------------------------------------+ |
178 | | Base 2 logarithm by a polynomial approximation. | | |
179 | | log2(x+1) | | |
180 | +---------------------------------------------------------------------------*/ | |
e8d591dc | 181 | static void log2_kernel(FPU_REG const *arg, u_char argsign, Xsig *accum_result, |
1da177e4 LT |
182 | long int *expon) |
183 | { | |
3d0d14f9 IM |
184 | long int exponent, adj; |
185 | unsigned long long Xsq; | |
186 | Xsig accumulator, Numer, Denom, argSignif, arg_signif; | |
187 | ||
188 | exponent = exponent16(arg); | |
189 | Numer.lsw = Denom.lsw = 0; | |
190 | XSIG_LL(Numer) = XSIG_LL(Denom) = significand(arg); | |
191 | if (argsign == SIGN_POS) { | |
192 | shr_Xsig(&Denom, 2 - (1 + exponent)); | |
193 | Denom.msw |= 0x80000000; | |
194 | div_Xsig(&Numer, &Denom, &argSignif); | |
195 | } else { | |
196 | shr_Xsig(&Denom, 1 - (1 + exponent)); | |
197 | negate_Xsig(&Denom); | |
198 | if (Denom.msw & 0x80000000) { | |
199 | div_Xsig(&Numer, &Denom, &argSignif); | |
200 | exponent++; | |
201 | } else { | |
202 | /* Denom must be 1.0 */ | |
203 | argSignif.lsw = Numer.lsw; | |
204 | argSignif.midw = Numer.midw; | |
205 | argSignif.msw = Numer.msw; | |
206 | } | |
1da177e4 | 207 | } |
1da177e4 LT |
208 | |
209 | #ifndef PECULIAR_486 | |
3d0d14f9 IM |
210 | /* Should check here that |local_arg| is within the valid range */ |
211 | if (exponent >= -2) { | |
212 | if ((exponent > -2) || (argSignif.msw > (unsigned)0xafb0ccc0)) { | |
213 | /* The argument is too large */ | |
214 | } | |
1da177e4 | 215 | } |
1da177e4 LT |
216 | #endif /* PECULIAR_486 */ |
217 | ||
3d0d14f9 IM |
218 | arg_signif.lsw = argSignif.lsw; |
219 | XSIG_LL(arg_signif) = XSIG_LL(argSignif); | |
220 | adj = norm_Xsig(&argSignif); | |
221 | accumulator.lsw = argSignif.lsw; | |
222 | XSIG_LL(accumulator) = XSIG_LL(argSignif); | |
223 | mul_Xsig_Xsig(&accumulator, &accumulator); | |
224 | shr_Xsig(&accumulator, 2 * (-1 - (1 + exponent + adj))); | |
225 | Xsq = XSIG_LL(accumulator); | |
226 | if (accumulator.lsw & 0x80000000) | |
227 | Xsq++; | |
228 | ||
229 | accumulator.msw = accumulator.midw = accumulator.lsw = 0; | |
230 | /* Do the basic fixed point polynomial evaluation */ | |
231 | polynomial_Xsig(&accumulator, &Xsq, logterms, HIPOWER - 1); | |
232 | ||
233 | mul_Xsig_Xsig(&accumulator, &argSignif); | |
234 | shr_Xsig(&accumulator, 6 - adj); | |
235 | ||
236 | mul32_Xsig(&arg_signif, leadterm); | |
237 | add_two_Xsig(&accumulator, &arg_signif, &exponent); | |
238 | ||
239 | *expon = exponent + 1; | |
240 | accum_result->lsw = accumulator.lsw; | |
241 | accum_result->midw = accumulator.midw; | |
242 | accum_result->msw = accumulator.msw; | |
1da177e4 LT |
243 | |
244 | } |