Botan: src/math/mp/mp_shift.cpp Source File

Botan 1.10.17

mp_shift.cpp
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1 /*
2 * MP Shift Algorithms
3 * (C) 1999-2007 Jack Lloyd
4 *
5 * Distributed under the terms of the Botan license
6 */
7
8 #include <botan/internal/mp_core.h>
9 #include <botan/mem_ops.h>
10
11 namespace Botan {
12
13 extern "C" {
14
15 /*
16 * Single Operand Left Shift
17 */
18 void bigint_shl1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
19 {
20 if(word_shift)
21 {
22 for(size_t j = 1; j != x_size + 1; ++j)
23 x[(x_size - j) + word_shift] = x[x_size - j];
24 clear_mem(x, word_shift);
25 }
26
27 if(bit_shift)
28 {
29 word carry = 0;
30 for(size_t j = word_shift; j != x_size + word_shift + 1; ++j)
31 {
32 word temp = x[j];
33 x[j] = (temp << bit_shift) | carry;
34 carry = (temp >> (MP_WORD_BITS - bit_shift));
35 }
36 }
37 }
38
39 /*
40 * Single Operand Right Shift
41 */
42 void bigint_shr1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
43 {
44 if(x_size < word_shift)
45 {
46 clear_mem(x, x_size);
47 return;
48 }
49
50 if(word_shift)
51 {
52 copy_mem(x, x + word_shift, x_size - word_shift);
53 clear_mem(x + x_size - word_shift, word_shift);
54 }
55
56 if(bit_shift)
57 {
58 word carry = 0;
59
60 size_t top = x_size - word_shift;
61
62 while(top >= 4)
63 {
64 word w = x[top-1];
65 x[top-1] = (w >> bit_shift) | carry;
66 carry = (w << (MP_WORD_BITS - bit_shift));
67
68 w = x[top-2];
69 x[top-2] = (w >> bit_shift) | carry;
70 carry = (w << (MP_WORD_BITS - bit_shift));
71
72 w = x[top-3];
73 x[top-3] = (w >> bit_shift) | carry;
74 carry = (w << (MP_WORD_BITS - bit_shift));
75
76 w = x[top-4];
77 x[top-4] = (w >> bit_shift) | carry;
78 carry = (w << (MP_WORD_BITS - bit_shift));
79
80 top -= 4;
81 }
82
83 while(top)
84 {
85 word w = x[top-1];
86 x[top-1] = (w >> bit_shift) | carry;
87 carry = (w << (MP_WORD_BITS - bit_shift));
88
89 top--;
90 }
91 }
92 }
93
94 /*
95 * Two Operand Left Shift
96 */
97 void bigint_shl2(word y[], const word x[], size_t x_size,
98 size_t word_shift, size_t bit_shift)
99 {
100 for(size_t j = 0; j != x_size; ++j)
101 y[j + word_shift] = x[j];
102 if(bit_shift)
103 {
104 word carry = 0;
105 for(size_t j = word_shift; j != x_size + word_shift + 1; ++j)
106 {
107 word w = y[j];
108 y[j] = (w << bit_shift) | carry;
109 carry = (w >> (MP_WORD_BITS - bit_shift));
110 }
111 }
112 }
113
114 /*
115 * Two Operand Right Shift
116 */
117 void bigint_shr2(word y[], const word x[], size_t x_size,
118 size_t word_shift, size_t bit_shift)
119 {
120 if(x_size < word_shift) return;
121
122 for(size_t j = 0; j != x_size - word_shift; ++j)
123 y[j] = x[j + word_shift];
124 if(bit_shift)
125 {
126 word carry = 0;
127 for(size_t j = x_size - word_shift; j > 0; --j)
128 {
129 word w = y[j-1];
130 y[j-1] = (w >> bit_shift) | carry;
131 carry = (w << (MP_WORD_BITS - bit_shift));
132 }
133 }
134 }
135
136 }
137
138 }
Botan::bigint_shr1
void bigint_shr1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
Definition: mp_shift.cpp:42
Botan::bigint_shr2
void bigint_shr2(word y[], const word x[], size_t x_size, size_t word_shift, size_t bit_shift)
Definition: mp_shift.cpp:117
Botan::clear_mem
void clear_mem(T *ptr, size_t n)
Definition: mem_ops.h:32
Botan::copy_mem
void copy_mem(T *out, const T *in, size_t n)
Definition: mem_ops.h:22
Botan
Definition: algo_base.h:14
Botan::bigint_shl2
void bigint_shl2(word y[], const word x[], size_t x_size, size_t word_shift, size_t bit_shift)
Definition: mp_shift.cpp:97
Botan::bigint_shl1
void bigint_shl1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
Definition: mp_shift.cpp:18
Botan::MP_WORD_BITS
const size_t MP_WORD_BITS
Definition: mp_core.h:18