1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
6  * biastest.c -- bias test for arc4random_uniform().
9  * (3/4) * UINT32_MAX, which should give a high amount of bias in
41 	fprintf(stderr, "usage: %s [-n tries] [-t upper_bound]\n", argv0);  in usage()
48 	uint32_t threshold = 3UL << 30;  in main()  local
59 			threshold = (uint32_t)atoll(optarg);  in main()
69 	if (threshold == 0) {  in main()
70 		fprintf(stderr, "threshold must be between 1 and %lu\n", (unsigned long)UINT32_MAX);  in main()
74 	sample = calloc(threshold, 1);  in main()
76 		perror("calloc(threshold, 1)");  in main()
80 	collect_sample(sample, tries, threshold);  in main()
81 	analyze_sample(sample, tries, threshold);  in main()
99 collect_sample(unsigned char *sample, long long tries, uint32_t threshold)  in collect_sample()  argument
108 		x = arc4random_uniform(threshold);  in collect_sample()
110 		assert(x < threshold);  in collect_sample()
127 analyze_sample(const unsigned char *sample, long long tries,  uint32_t threshold)  in analyze_sample()  argument
138 	for (i = 0; i < threshold; i++) {  in analyze_sample()
146 	median = threshold;  in analyze_sample()
153 	for (i = 0; i < threshold; i++) {  in analyze_sample()
154 		discrepancy = i - average;  in analyze_sample()
158 		if (median == threshold && n > tries / 2)  in analyze_sample()
171 	assert(median < threshold);  in analyze_sample()
173 	printf("\tthreshold:	%lu\n", (unsigned long)threshold);  in analyze_sample()
177 	printf("\tmedian:		%lld (expected %lu)\n", median, (unsigned long)threshold / 2);  in analyze_sample()
178 	printf("\taverage:	%f (expected %f)\n", average, 0.5 * (threshold - 1));  in analyze_sample()
180 	    sqrt(((double)threshold * threshold - 1.0) / 12));  in analyze_sample()
186 	average = (double)tries / threshold;  in analyze_sample()
190 		discrepancy = i - average;  in analyze_sample()
194 	variance /= threshold;  in analyze_sample()
200 		if (n >= threshold / 2) {  in analyze_sample()
210 …printf("\tdeviation:	%f (expected %f)\n\n", sqrt(variance), sqrt(average * (1.0 - 1.0 / threshold)…  in analyze_sample()