1 /* mpz_addmul_ui, mpz_submul_ui - add or subtract small multiple.
2
3 THE mpz_aorsmul_1 FUNCTION IN THIS FILE IS FOR INTERNAL USE ONLY AND IS
4 ALMOST CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR
5 COMPLETELY IN FUTURE GNU MP RELEASES.
6
7 Copyright 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
8
9 This file is part of the GNU MP Library.
10
11 The GNU MP Library is free software; you can redistribute it and/or modify
12 it under the terms of the GNU Lesser General Public License as published by
13 the Free Software Foundation; either version 3 of the License, or (at your
14 option) any later version.
15
16 The GNU MP Library is distributed in the hope that it will be useful, but
17 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
18 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
19 License for more details.
20
21 You should have received a copy of the GNU Lesser General Public License
22 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
23
24 #include "gmp.h"
25 #include "gmp-impl.h"
26
27
28 #if HAVE_NATIVE_mpn_mul_1c
29 #define MPN_MUL_1C(cout, dst, src, size, n, cin) \
30 do { \
31 (cout) = mpn_mul_1c (dst, src, size, n, cin); \
32 } while (0)
33 #else
34 #define MPN_MUL_1C(cout, dst, src, size, n, cin) \
35 do { \
36 mp_limb_t __cy; \
37 __cy = mpn_mul_1 (dst, src, size, n); \
38 (cout) = __cy + mpn_add_1 (dst, dst, size, cin); \
39 } while (0)
40 #endif
41
42
43 /* sub>=0 means an addmul w += x*y, sub<0 means a submul w -= x*y.
44
45 All that's needed to account for negative w or x is to flip "sub".
46
47 The final w will retain its sign, unless an underflow occurs in a submul
48 of absolute values, in which case it's flipped.
49
50 If x has more limbs than w, then mpn_submul_1 followed by mpn_com is
51 used. The alternative would be mpn_mul_1 into temporary space followed
52 by mpn_sub_n. Avoiding temporary space seem good, and submul+com stands
53 a chance of being faster since it involves only one set of carry
54 propagations, not two. Note that doing an addmul_1 with a
55 twos-complement negative y doesn't work, because it effectively adds an
56 extra x * 2^GMP_LIMB_BITS. */
57
58 REGPARM_ATTR(1) void
mpz_aorsmul_1(mpz_ptr w,mpz_srcptr x,mp_limb_t y,mp_size_t sub)59 mpz_aorsmul_1 (mpz_ptr w, mpz_srcptr x, mp_limb_t y, mp_size_t sub)
60 {
61 mp_size_t xsize, wsize, wsize_signed, new_wsize, min_size, dsize;
62 mp_srcptr xp;
63 mp_ptr wp;
64 mp_limb_t cy;
65
66 /* w unaffected if x==0 or y==0 */
67 xsize = SIZ (x);
68 if (xsize == 0 || y == 0)
69 return;
70
71 sub ^= xsize;
72 xsize = ABS (xsize);
73
74 wsize_signed = SIZ (w);
75 if (wsize_signed == 0)
76 {
77 /* nothing to add to, just set x*y, "sub" gives the sign */
78 MPZ_REALLOC (w, xsize+1);
79 wp = PTR (w);
80 cy = mpn_mul_1 (wp, PTR(x), xsize, y);
81 wp[xsize] = cy;
82 xsize += (cy != 0);
83 SIZ (w) = (sub >= 0 ? xsize : -xsize);
84 return;
85 }
86
87 sub ^= wsize_signed;
88 wsize = ABS (wsize_signed);
89
90 new_wsize = MAX (wsize, xsize);
91 MPZ_REALLOC (w, new_wsize+1);
92 wp = PTR (w);
93 xp = PTR (x);
94 min_size = MIN (wsize, xsize);
95
96 if (sub >= 0)
97 {
98 /* addmul of absolute values */
99
100 cy = mpn_addmul_1 (wp, xp, min_size, y);
101 wp += min_size;
102 xp += min_size;
103
104 dsize = xsize - wsize;
105 #if HAVE_NATIVE_mpn_mul_1c
106 if (dsize > 0)
107 cy = mpn_mul_1c (wp, xp, dsize, y, cy);
108 else if (dsize < 0)
109 {
110 dsize = -dsize;
111 cy = mpn_add_1 (wp, wp, dsize, cy);
112 }
113 #else
114 if (dsize != 0)
115 {
116 mp_limb_t cy2;
117 if (dsize > 0)
118 cy2 = mpn_mul_1 (wp, xp, dsize, y);
119 else
120 {
121 dsize = -dsize;
122 cy2 = 0;
123 }
124 cy = cy2 + mpn_add_1 (wp, wp, dsize, cy);
125 }
126 #endif
127
128 wp[dsize] = cy;
129 new_wsize += (cy != 0);
130 }
131 else
132 {
133 /* submul of absolute values */
134
135 cy = mpn_submul_1 (wp, xp, min_size, y);
136 if (wsize >= xsize)
137 {
138 /* if w bigger than x, then propagate borrow through it */
139 if (wsize != xsize)
140 cy = mpn_sub_1 (wp+xsize, wp+xsize, wsize-xsize, cy);
141
142 if (cy != 0)
143 {
144 /* Borrow out of w, take twos complement negative to get
145 absolute value, flip sign of w. */
146 wp[new_wsize] = ~-cy; /* extra limb is 0-cy */
147 mpn_com (wp, wp, new_wsize);
148 new_wsize++;
149 MPN_INCR_U (wp, new_wsize, CNST_LIMB(1));
150 wsize_signed = -wsize_signed;
151 }
152 }
153 else /* wsize < xsize */
154 {
155 /* x bigger than w, so want x*y-w. Submul has given w-x*y, so
156 take twos complement and use an mpn_mul_1 for the rest. */
157
158 mp_limb_t cy2;
159
160 /* -(-cy*b^n + w-x*y) = (cy-1)*b^n + ~(w-x*y) + 1 */
161 mpn_com (wp, wp, wsize);
162 cy += mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
163 cy -= 1;
164
165 /* If cy-1 == -1 then hold that -1 for latter. mpn_submul_1 never
166 returns cy==MP_LIMB_T_MAX so that value always indicates a -1. */
167 cy2 = (cy == MP_LIMB_T_MAX);
168 cy += cy2;
169 MPN_MUL_1C (cy, wp+wsize, xp+wsize, xsize-wsize, y, cy);
170 wp[new_wsize] = cy;
171 new_wsize += (cy != 0);
172
173 /* Apply any -1 from above. The value at wp+wsize is non-zero
174 because y!=0 and the high limb of x will be non-zero. */
175 if (cy2)
176 MPN_DECR_U (wp+wsize, new_wsize-wsize, CNST_LIMB(1));
177
178 wsize_signed = -wsize_signed;
179 }
180
181 /* submul can produce high zero limbs due to cancellation, both when w
182 has more limbs or x has more */
183 MPN_NORMALIZE (wp, new_wsize);
184 }
185
186 SIZ (w) = (wsize_signed >= 0 ? new_wsize : -new_wsize);
187
188 ASSERT (new_wsize == 0 || PTR(w)[new_wsize-1] != 0);
189 }
190
191
192 void
mpz_addmul_ui(mpz_ptr w,mpz_srcptr x,unsigned long y)193 mpz_addmul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y)
194 {
195 #if BITS_PER_ULONG > GMP_NUMB_BITS
196 if (UNLIKELY (y > GMP_NUMB_MAX && SIZ(x) != 0))
197 {
198 mpz_t t;
199 mp_ptr tp;
200 mp_size_t xn;
201 TMP_DECL;
202 TMP_MARK;
203 xn = SIZ (x);
204 MPZ_TMP_INIT (t, ABS (xn) + 1);
205 tp = PTR (t);
206 tp[0] = 0;
207 MPN_COPY (tp + 1, PTR(x), ABS (xn));
208 SIZ(t) = xn >= 0 ? xn + 1 : xn - 1;
209 mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) 0);
210 PTR(t) = tp + 1;
211 SIZ(t) = xn;
212 mpz_aorsmul_1 (w, t, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) 0);
213 TMP_FREE;
214 return;
215 }
216 #endif
217 mpz_aorsmul_1 (w, x, (mp_limb_t) y, (mp_size_t) 0);
218 }
219
220 void
mpz_submul_ui(mpz_ptr w,mpz_srcptr x,unsigned long y)221 mpz_submul_ui (mpz_ptr w, mpz_srcptr x, unsigned long y)
222 {
223 #if BITS_PER_ULONG > GMP_NUMB_BITS
224 if (y > GMP_NUMB_MAX && SIZ(x) != 0)
225 {
226 mpz_t t;
227 mp_ptr tp;
228 mp_size_t xn;
229 TMP_DECL;
230 TMP_MARK;
231 xn = SIZ (x);
232 MPZ_TMP_INIT (t, ABS (xn) + 1);
233 tp = PTR (t);
234 tp[0] = 0;
235 MPN_COPY (tp + 1, PTR(x), ABS (xn));
236 SIZ(t) = xn >= 0 ? xn + 1 : xn - 1;
237 mpz_aorsmul_1 (w, t, (mp_limb_t) y >> GMP_NUMB_BITS, (mp_size_t) -1);
238 PTR(t) = tp + 1;
239 SIZ(t) = xn;
240 mpz_aorsmul_1 (w, t, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) -1);
241 TMP_FREE;
242 return;
243 }
244 #endif
245 mpz_aorsmul_1 (w, x, (mp_limb_t) y & GMP_NUMB_MASK, (mp_size_t) -1);
246 }
247