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1.1 maekawa 1: /* mpn_set_str (mp_ptr res_ptr, const char *str, size_t str_len, int base)
2: -- Convert a STR_LEN long base BASE byte string pointed to by STR to a
3: limb vector pointed to by RES_PTR. Return the number of limbs in
4: RES_PTR.
5:
6: Copyright (C) 1991, 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
7:
8: This file is part of the GNU MP Library.
9:
10: The GNU MP Library is free software; you can redistribute it and/or modify
11: it under the terms of the GNU Library General Public License as published by
12: the Free Software Foundation; either version 2 of the License, or (at your
13: option) any later version.
14:
15: The GNU MP Library is distributed in the hope that it will be useful, but
16: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
17: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
18: License for more details.
19:
20: You should have received a copy of the GNU Library General Public License
21: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
22: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
23: MA 02111-1307, USA. */
24:
25: #include "gmp.h"
26: #include "gmp-impl.h"
27:
28: mp_size_t
29: mpn_set_str (xp, str, str_len, base)
30: mp_ptr xp;
31: const unsigned char *str;
32: size_t str_len;
33: int base;
34: {
35: mp_size_t size;
36: mp_limb_t big_base;
37: int indigits_per_limb;
38: mp_limb_t res_digit;
39:
40: big_base = __mp_bases[base].big_base;
41: indigits_per_limb = __mp_bases[base].chars_per_limb;
42:
43: /* size = str_len / indigits_per_limb + 1; */
44:
45: size = 0;
46:
47: if ((base & (base - 1)) == 0)
48: {
49: /* The base is a power of 2. Read the input string from
50: least to most significant character/digit. */
51:
52: const unsigned char *s;
53: int next_bitpos;
54: int bits_per_indigit = big_base;
55:
56: res_digit = 0;
57: next_bitpos = 0;
58:
59: for (s = str + str_len - 1; s >= str; s--)
60: {
61: int inp_digit = *s;
62:
63: res_digit |= (mp_limb_t) inp_digit << next_bitpos;
64: next_bitpos += bits_per_indigit;
65: if (next_bitpos >= BITS_PER_MP_LIMB)
66: {
67: xp[size++] = res_digit;
68: next_bitpos -= BITS_PER_MP_LIMB;
69: res_digit = inp_digit >> (bits_per_indigit - next_bitpos);
70: }
71: }
72:
73: if (res_digit != 0)
74: xp[size++] = res_digit;
75: }
76: else
77: {
78: /* General case. The base is not a power of 2. */
79:
80: size_t i;
81: int j;
82: mp_limb_t cy_limb;
83:
84: for (i = indigits_per_limb; i < str_len; i += indigits_per_limb)
85: {
86: res_digit = *str++;
87: if (base == 10)
88: { /* This is a common case.
89: Help the compiler to avoid multiplication. */
90: for (j = 1; j < indigits_per_limb; j++)
91: res_digit = res_digit * 10 + *str++;
92: }
93: else
94: {
95: for (j = 1; j < indigits_per_limb; j++)
96: res_digit = res_digit * base + *str++;
97: }
98:
99: if (size == 0)
100: {
101: if (res_digit != 0)
102: {
103: xp[0] = res_digit;
104: size = 1;
105: }
106: }
107: else
108: {
109: cy_limb = mpn_mul_1 (xp, xp, size, big_base);
110: cy_limb += mpn_add_1 (xp, xp, size, res_digit);
111: if (cy_limb != 0)
112: xp[size++] = cy_limb;
113: }
114: }
115:
116: big_base = base;
117: res_digit = *str++;
118: if (base == 10)
119: { /* This is a common case.
120: Help the compiler to avoid multiplication. */
121: for (j = 1; j < str_len - (i - indigits_per_limb); j++)
122: {
123: res_digit = res_digit * 10 + *str++;
124: big_base *= 10;
125: }
126: }
127: else
128: {
129: for (j = 1; j < str_len - (i - indigits_per_limb); j++)
130: {
131: res_digit = res_digit * base + *str++;
132: big_base *= base;
133: }
134: }
135:
136: if (size == 0)
137: {
138: if (res_digit != 0)
139: {
140: xp[0] = res_digit;
141: size = 1;
142: }
143: }
144: else
145: {
146: cy_limb = mpn_mul_1 (xp, xp, size, big_base);
147: cy_limb += mpn_add_1 (xp, xp, size, res_digit);
148: if (cy_limb != 0)
149: xp[size++] = cy_limb;
150: }
151: }
152:
153: return size;
154: }