1 #include "sc.h"
2 #include "crypto_int64.h"
3 #include "crypto_uint32.h"
4 #include "crypto_uint64.h"
5 
load_3(const unsigned char * in)6 static crypto_uint64 load_3(const unsigned char *in)
7 {
8   crypto_uint64 result;
9   result = (crypto_uint64) in[0];
10   result |= ((crypto_uint64) in[1]) << 8;
11   result |= ((crypto_uint64) in[2]) << 16;
12   return result;
13 }
14 
load_4(const unsigned char * in)15 static crypto_uint64 load_4(const unsigned char *in)
16 {
17   crypto_uint64 result;
18   result = (crypto_uint64) in[0];
19   result |= ((crypto_uint64) in[1]) << 8;
20   result |= ((crypto_uint64) in[2]) << 16;
21   result |= ((crypto_uint64) in[3]) << 24;
22   return result;
23 }
24 
25 /*
26 Input:
27   s[0]+256*s[1]+...+256^63*s[63] = s
28 
29 Output:
30   s[0]+256*s[1]+...+256^31*s[31] = s mod l
31   where l = 2^252 + 27742317777372353535851937790883648493.
32   Overwrites s in place.
33 */
34 
sc_reduce(unsigned char * s)35 void sc_reduce(unsigned char *s)
36 {
37   crypto_int64 s0 = 2097151 & load_3(s);
38   crypto_int64 s1 = 2097151 & (load_4(s + 2) >> 5);
39   crypto_int64 s2 = 2097151 & (load_3(s + 5) >> 2);
40   crypto_int64 s3 = 2097151 & (load_4(s + 7) >> 7);
41   crypto_int64 s4 = 2097151 & (load_4(s + 10) >> 4);
42   crypto_int64 s5 = 2097151 & (load_3(s + 13) >> 1);
43   crypto_int64 s6 = 2097151 & (load_4(s + 15) >> 6);
44   crypto_int64 s7 = 2097151 & (load_3(s + 18) >> 3);
45   crypto_int64 s8 = 2097151 & load_3(s + 21);
46   crypto_int64 s9 = 2097151 & (load_4(s + 23) >> 5);
47   crypto_int64 s10 = 2097151 & (load_3(s + 26) >> 2);
48   crypto_int64 s11 = 2097151 & (load_4(s + 28) >> 7);
49   crypto_int64 s12 = 2097151 & (load_4(s + 31) >> 4);
50   crypto_int64 s13 = 2097151 & (load_3(s + 34) >> 1);
51   crypto_int64 s14 = 2097151 & (load_4(s + 36) >> 6);
52   crypto_int64 s15 = 2097151 & (load_3(s + 39) >> 3);
53   crypto_int64 s16 = 2097151 & load_3(s + 42);
54   crypto_int64 s17 = 2097151 & (load_4(s + 44) >> 5);
55   crypto_int64 s18 = 2097151 & (load_3(s + 47) >> 2);
56   crypto_int64 s19 = 2097151 & (load_4(s + 49) >> 7);
57   crypto_int64 s20 = 2097151 & (load_4(s + 52) >> 4);
58   crypto_int64 s21 = 2097151 & (load_3(s + 55) >> 1);
59   crypto_int64 s22 = 2097151 & (load_4(s + 57) >> 6);
60   crypto_int64 s23 = (load_4(s + 60) >> 3);
61   crypto_int64 carry0;
62   crypto_int64 carry1;
63   crypto_int64 carry2;
64   crypto_int64 carry3;
65   crypto_int64 carry4;
66   crypto_int64 carry5;
67   crypto_int64 carry6;
68   crypto_int64 carry7;
69   crypto_int64 carry8;
70   crypto_int64 carry9;
71   crypto_int64 carry10;
72   crypto_int64 carry11;
73   crypto_int64 carry12;
74   crypto_int64 carry13;
75   crypto_int64 carry14;
76   crypto_int64 carry15;
77   crypto_int64 carry16;
78 
79   s11 += s23 * 666643;
80   s12 += s23 * 470296;
81   s13 += s23 * 654183;
82   s14 -= s23 * 997805;
83   s15 += s23 * 136657;
84   s16 -= s23 * 683901;
85   s23 = 0;
86 
87   s10 += s22 * 666643;
88   s11 += s22 * 470296;
89   s12 += s22 * 654183;
90   s13 -= s22 * 997805;
91   s14 += s22 * 136657;
92   s15 -= s22 * 683901;
93   s22 = 0;
94 
95   s9 += s21 * 666643;
96   s10 += s21 * 470296;
97   s11 += s21 * 654183;
98   s12 -= s21 * 997805;
99   s13 += s21 * 136657;
100   s14 -= s21 * 683901;
101   s21 = 0;
102 
103   s8 += s20 * 666643;
104   s9 += s20 * 470296;
105   s10 += s20 * 654183;
106   s11 -= s20 * 997805;
107   s12 += s20 * 136657;
108   s13 -= s20 * 683901;
109   s20 = 0;
110 
111   s7 += s19 * 666643;
112   s8 += s19 * 470296;
113   s9 += s19 * 654183;
114   s10 -= s19 * 997805;
115   s11 += s19 * 136657;
116   s12 -= s19 * 683901;
117   s19 = 0;
118 
119   s6 += s18 * 666643;
120   s7 += s18 * 470296;
121   s8 += s18 * 654183;
122   s9 -= s18 * 997805;
123   s10 += s18 * 136657;
124   s11 -= s18 * 683901;
125   s18 = 0;
126 
127   carry6 = (s6 + (1<<20)) >> 21; s7 += carry6; s6 -= carry6 << 21;
128   carry8 = (s8 + (1<<20)) >> 21; s9 += carry8; s8 -= carry8 << 21;
129   carry10 = (s10 + (1<<20)) >> 21; s11 += carry10; s10 -= carry10 << 21;
130   carry12 = (s12 + (1<<20)) >> 21; s13 += carry12; s12 -= carry12 << 21;
131   carry14 = (s14 + (1<<20)) >> 21; s15 += carry14; s14 -= carry14 << 21;
132   carry16 = (s16 + (1<<20)) >> 21; s17 += carry16; s16 -= carry16 << 21;
133 
134   carry7 = (s7 + (1<<20)) >> 21; s8 += carry7; s7 -= carry7 << 21;
135   carry9 = (s9 + (1<<20)) >> 21; s10 += carry9; s9 -= carry9 << 21;
136   carry11 = (s11 + (1<<20)) >> 21; s12 += carry11; s11 -= carry11 << 21;
137   carry13 = (s13 + (1<<20)) >> 21; s14 += carry13; s13 -= carry13 << 21;
138   carry15 = (s15 + (1<<20)) >> 21; s16 += carry15; s15 -= carry15 << 21;
139 
140   s5 += s17 * 666643;
141   s6 += s17 * 470296;
142   s7 += s17 * 654183;
143   s8 -= s17 * 997805;
144   s9 += s17 * 136657;
145   s10 -= s17 * 683901;
146   s17 = 0;
147 
148   s4 += s16 * 666643;
149   s5 += s16 * 470296;
150   s6 += s16 * 654183;
151   s7 -= s16 * 997805;
152   s8 += s16 * 136657;
153   s9 -= s16 * 683901;
154   s16 = 0;
155 
156   s3 += s15 * 666643;
157   s4 += s15 * 470296;
158   s5 += s15 * 654183;
159   s6 -= s15 * 997805;
160   s7 += s15 * 136657;
161   s8 -= s15 * 683901;
162   s15 = 0;
163 
164   s2 += s14 * 666643;
165   s3 += s14 * 470296;
166   s4 += s14 * 654183;
167   s5 -= s14 * 997805;
168   s6 += s14 * 136657;
169   s7 -= s14 * 683901;
170   s14 = 0;
171 
172   s1 += s13 * 666643;
173   s2 += s13 * 470296;
174   s3 += s13 * 654183;
175   s4 -= s13 * 997805;
176   s5 += s13 * 136657;
177   s6 -= s13 * 683901;
178   s13 = 0;
179 
180   s0 += s12 * 666643;
181   s1 += s12 * 470296;
182   s2 += s12 * 654183;
183   s3 -= s12 * 997805;
184   s4 += s12 * 136657;
185   s5 -= s12 * 683901;
186   s12 = 0;
187 
188   carry0 = (s0 + (1<<20)) >> 21; s1 += carry0; s0 -= carry0 << 21;
189   carry2 = (s2 + (1<<20)) >> 21; s3 += carry2; s2 -= carry2 << 21;
190   carry4 = (s4 + (1<<20)) >> 21; s5 += carry4; s4 -= carry4 << 21;
191   carry6 = (s6 + (1<<20)) >> 21; s7 += carry6; s6 -= carry6 << 21;
192   carry8 = (s8 + (1<<20)) >> 21; s9 += carry8; s8 -= carry8 << 21;
193   carry10 = (s10 + (1<<20)) >> 21; s11 += carry10; s10 -= carry10 << 21;
194 
195   carry1 = (s1 + (1<<20)) >> 21; s2 += carry1; s1 -= carry1 << 21;
196   carry3 = (s3 + (1<<20)) >> 21; s4 += carry3; s3 -= carry3 << 21;
197   carry5 = (s5 + (1<<20)) >> 21; s6 += carry5; s5 -= carry5 << 21;
198   carry7 = (s7 + (1<<20)) >> 21; s8 += carry7; s7 -= carry7 << 21;
199   carry9 = (s9 + (1<<20)) >> 21; s10 += carry9; s9 -= carry9 << 21;
200   carry11 = (s11 + (1<<20)) >> 21; s12 += carry11; s11 -= carry11 << 21;
201 
202   s0 += s12 * 666643;
203   s1 += s12 * 470296;
204   s2 += s12 * 654183;
205   s3 -= s12 * 997805;
206   s4 += s12 * 136657;
207   s5 -= s12 * 683901;
208   s12 = 0;
209 
210   carry0 = s0 >> 21; s1 += carry0; s0 -= carry0 << 21;
211   carry1 = s1 >> 21; s2 += carry1; s1 -= carry1 << 21;
212   carry2 = s2 >> 21; s3 += carry2; s2 -= carry2 << 21;
213   carry3 = s3 >> 21; s4 += carry3; s3 -= carry3 << 21;
214   carry4 = s4 >> 21; s5 += carry4; s4 -= carry4 << 21;
215   carry5 = s5 >> 21; s6 += carry5; s5 -= carry5 << 21;
216   carry6 = s6 >> 21; s7 += carry6; s6 -= carry6 << 21;
217   carry7 = s7 >> 21; s8 += carry7; s7 -= carry7 << 21;
218   carry8 = s8 >> 21; s9 += carry8; s8 -= carry8 << 21;
219   carry9 = s9 >> 21; s10 += carry9; s9 -= carry9 << 21;
220   carry10 = s10 >> 21; s11 += carry10; s10 -= carry10 << 21;
221   carry11 = s11 >> 21; s12 += carry11; s11 -= carry11 << 21;
222 
223   s0 += s12 * 666643;
224   s1 += s12 * 470296;
225   s2 += s12 * 654183;
226   s3 -= s12 * 997805;
227   s4 += s12 * 136657;
228   s5 -= s12 * 683901;
229   s12 = 0;
230 
231   carry0 = s0 >> 21; s1 += carry0; s0 -= carry0 << 21;
232   carry1 = s1 >> 21; s2 += carry1; s1 -= carry1 << 21;
233   carry2 = s2 >> 21; s3 += carry2; s2 -= carry2 << 21;
234   carry3 = s3 >> 21; s4 += carry3; s3 -= carry3 << 21;
235   carry4 = s4 >> 21; s5 += carry4; s4 -= carry4 << 21;
236   carry5 = s5 >> 21; s6 += carry5; s5 -= carry5 << 21;
237   carry6 = s6 >> 21; s7 += carry6; s6 -= carry6 << 21;
238   carry7 = s7 >> 21; s8 += carry7; s7 -= carry7 << 21;
239   carry8 = s8 >> 21; s9 += carry8; s8 -= carry8 << 21;
240   carry9 = s9 >> 21; s10 += carry9; s9 -= carry9 << 21;
241   carry10 = s10 >> 21; s11 += carry10; s10 -= carry10 << 21;
242 
243   s[0] = s0 >> 0;
244   s[1] = s0 >> 8;
245   s[2] = (s0 >> 16) | (s1 << 5);
246   s[3] = s1 >> 3;
247   s[4] = s1 >> 11;
248   s[5] = (s1 >> 19) | (s2 << 2);
249   s[6] = s2 >> 6;
250   s[7] = (s2 >> 14) | (s3 << 7);
251   s[8] = s3 >> 1;
252   s[9] = s3 >> 9;
253   s[10] = (s3 >> 17) | (s4 << 4);
254   s[11] = s4 >> 4;
255   s[12] = s4 >> 12;
256   s[13] = (s4 >> 20) | (s5 << 1);
257   s[14] = s5 >> 7;
258   s[15] = (s5 >> 15) | (s6 << 6);
259   s[16] = s6 >> 2;
260   s[17] = s6 >> 10;
261   s[18] = (s6 >> 18) | (s7 << 3);
262   s[19] = s7 >> 5;
263   s[20] = s7 >> 13;
264   s[21] = s8 >> 0;
265   s[22] = s8 >> 8;
266   s[23] = (s8 >> 16) | (s9 << 5);
267   s[24] = s9 >> 3;
268   s[25] = s9 >> 11;
269   s[26] = (s9 >> 19) | (s10 << 2);
270   s[27] = s10 >> 6;
271   s[28] = (s10 >> 14) | (s11 << 7);
272   s[29] = s11 >> 1;
273   s[30] = s11 >> 9;
274   s[31] = s11 >> 17;
275 }
276