1 /* mpf_ui_sub -- Subtract a float from an unsigned long int.
2
3 Copyright 1993-1996, 2001, 2002, 2005, 2014 Free Software Foundation, Inc.
4
5 This file is part of the GNU MP Library.
6
7 The GNU MP Library is free software; you can redistribute it and/or modify
8 it under the terms of either:
9
10 * the GNU Lesser General Public License as published by the Free
11 Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
13
14 or
15
16 * the GNU General Public License as published by the Free Software
17 Foundation; either version 2 of the License, or (at your option) any
18 later version.
19
20 or both in parallel, as here.
21
22 The GNU MP Library is distributed in the hope that it will be useful, but
23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
24 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
25 for more details.
26
27 You should have received copies of the GNU General Public License and the
28 GNU Lesser General Public License along with the GNU MP Library. If not,
29 see https://www.gnu.org/licenses/. */
30
31 #include "gmp-impl.h"
32
33 void
mpf_ui_sub(mpf_ptr r,unsigned long int u,mpf_srcptr v)34 mpf_ui_sub (mpf_ptr r, unsigned long int u, mpf_srcptr v)
35 {
36 #if 1
37 __mpf_struct uu;
38 mp_limb_t ul;
39
40 if (u == 0)
41 {
42 mpf_neg (r, v);
43 return;
44 }
45
46 ul = u;
47 uu._mp_size = 1;
48 uu._mp_d = &ul;
49 uu._mp_exp = 1;
50 mpf_sub (r, &uu, v);
51
52 #else
53 mp_srcptr up, vp;
54 mp_ptr rp, tp;
55 mp_size_t usize, vsize, rsize;
56 mp_size_t prec;
57 mp_exp_t uexp;
58 mp_size_t ediff;
59 int negate;
60 mp_limb_t ulimb;
61 TMP_DECL;
62
63 vsize = v->_mp_size;
64
65 /* Handle special cases that don't work in generic code below. */
66 if (u == 0)
67 {
68 mpf_neg (r, v);
69 return;
70 }
71 if (vsize == 0)
72 {
73 mpf_set_ui (r, u);
74 return;
75 }
76
77 /* If signs of U and V are different, perform addition. */
78 if (vsize < 0)
79 {
80 __mpf_struct v_negated;
81 v_negated._mp_size = -vsize;
82 v_negated._mp_exp = v->_mp_exp;
83 v_negated._mp_d = v->_mp_d;
84 mpf_add_ui (r, &v_negated, u);
85 return;
86 }
87
88 /* Signs are now known to be the same. */
89 ASSERT (vsize > 0);
90 ulimb = u;
91 /* Make U be the operand with the largest exponent. */
92 negate = 1 < v->_mp_exp;
93 prec = r->_mp_prec + negate;
94 rp = r->_mp_d;
95 if (negate)
96 {
97 usize = vsize;
98 vsize = 1;
99 up = v->_mp_d;
100 vp = &ulimb;
101 uexp = v->_mp_exp;
102 ediff = uexp - 1;
103
104 /* If U extends beyond PREC, ignore the part that does. */
105 if (usize > prec)
106 {
107 up += usize - prec;
108 usize = prec;
109 }
110 ASSERT (ediff > 0);
111 }
112 else
113 {
114 vp = v->_mp_d;
115 ediff = 1 - v->_mp_exp;
116 /* Ignore leading limbs in U and V that are equal. Doing
117 this helps increase the precision of the result. */
118 if (ediff == 0 && ulimb == vp[vsize - 1])
119 {
120 usize = 0;
121 vsize--;
122 uexp = 0;
123 /* Note that V might now have leading zero limbs.
124 In that case we have to adjust uexp. */
125 for (;;)
126 {
127 if (vsize == 0) {
128 rsize = 0;
129 uexp = 0;
130 goto done;
131 }
132 if ( vp[vsize - 1] != 0)
133 break;
134 vsize--, uexp--;
135 }
136 }
137 else
138 {
139 usize = 1;
140 uexp = 1;
141 up = &ulimb;
142 }
143 ASSERT (usize <= prec);
144 }
145
146 if (ediff >= prec)
147 {
148 /* V completely cancelled. */
149 if (rp != up)
150 MPN_COPY (rp, up, usize);
151 rsize = usize;
152 }
153 else
154 {
155 /* If V extends beyond PREC, ignore the part that does.
156 Note that this can make vsize neither zero nor negative. */
157 if (vsize + ediff > prec)
158 {
159 vp += vsize + ediff - prec;
160 vsize = prec - ediff;
161 }
162
163 /* Locate the least significant non-zero limb in (the needed
164 parts of) U and V, to simplify the code below. */
165 ASSERT (vsize > 0);
166 for (;;)
167 {
168 if (vp[0] != 0)
169 break;
170 vp++, vsize--;
171 if (vsize == 0)
172 {
173 MPN_COPY (rp, up, usize);
174 rsize = usize;
175 goto done;
176 }
177 }
178 for (;;)
179 {
180 if (usize == 0)
181 {
182 MPN_COPY (rp, vp, vsize);
183 rsize = vsize;
184 negate ^= 1;
185 goto done;
186 }
187 if (up[0] != 0)
188 break;
189 up++, usize--;
190 }
191
192 ASSERT (usize > 0 && vsize > 0);
193 TMP_MARK;
194
195 tp = TMP_ALLOC_LIMBS (prec);
196
197 /* uuuu | uuuu | uuuu | uuuu | uuuu */
198 /* vvvvvvv | vv | vvvvv | v | vv */
199
200 if (usize > ediff)
201 {
202 /* U and V partially overlaps. */
203 if (ediff == 0)
204 {
205 ASSERT (usize == 1 && vsize >= 1 && ulimb == *up); /* usize is 1>ediff, vsize >= 1 */
206 if (1 < vsize)
207 {
208 /* u */
209 /* vvvvvvv */
210 rsize = vsize;
211 vsize -= 1;
212 /* mpn_cmp (up, vp + vsize - usize, usize) > 0 */
213 if (ulimb > vp[vsize])
214 {
215 tp[vsize] = ulimb - vp[vsize] - 1;
216 ASSERT_CARRY (mpn_neg (tp, vp, vsize));
217 }
218 else
219 {
220 /* vvvvvvv */ /* Swap U and V. */
221 /* u */
222 MPN_COPY (tp, vp, vsize);
223 tp[vsize] = vp[vsize] - ulimb;
224 negate = 1;
225 }
226 }
227 else /* vsize == usize == 1 */
228 {
229 /* u */
230 /* v */
231 rsize = 1;
232 negate = ulimb < vp[0];
233 tp[0] = negate ? vp[0] - ulimb: ulimb - vp[0];
234 }
235 }
236 else
237 {
238 ASSERT (vsize + ediff <= usize);
239 ASSERT (vsize == 1 && usize >= 2 && ulimb == *vp);
240 {
241 /* uuuu */
242 /* v */
243 mp_size_t size;
244 size = usize - ediff - 1;
245 MPN_COPY (tp, up, size);
246 ASSERT_NOCARRY (mpn_sub_1 (tp + size, up + size, usize - size, ulimb));
247 rsize = usize;
248 }
249 /* Other cases are not possible */
250 /* uuuu */
251 /* vvvvv */
252 }
253 }
254 else
255 {
256 /* uuuu */
257 /* vv */
258 mp_size_t size, i;
259 ASSERT_CARRY (mpn_neg (tp, vp, vsize));
260 rsize = vsize + ediff;
261 size = rsize - usize;
262 for (i = vsize; i < size; i++)
263 tp[i] = GMP_NUMB_MAX;
264 ASSERT_NOCARRY (mpn_sub_1 (tp + size, up, usize, CNST_LIMB (1)));
265 }
266
267 /* Full normalize. Optimize later. */
268 while (rsize != 0 && tp[rsize - 1] == 0)
269 {
270 rsize--;
271 uexp--;
272 }
273 MPN_COPY (rp, tp, rsize);
274 TMP_FREE;
275 }
276
277 done:
278 r->_mp_size = negate ? -rsize : rsize;
279 r->_mp_exp = uexp;
280 #endif
281 }
282