rework code to be more accurate and platform-independent

src/main.c

@@ -1,60 +1,61 @@
-#include <features.h>
-#if _POSIX_C_SOURCE >= 199309L
-# include <bits/time.h>
-# include <errno.h>
-# include <limits.h>
-# include <stdarg.h>
-# include <stdint.h>
-# include <stdio.h>
-# include <stdlib.h>
-# include <stdnoreturn.h>
-# include <time.h>
+#include <bits/time.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
 
-noreturn static inline void error(char* fmt, ...) {
-	va_list args;
-	va_start(args, fmt);
-	vfprintf(stderr, fmt, args);
-	va_end(args);
-	exit(1);
+#define error(ret, s, ...)                   \
+	do {                                     \
+		fprintf(stderr, (s), ##__VA_ARGS__); \
+		exit(ret);                           \
+	} while (0)
+
+typedef unsigned long long ull;
+
+/* acquires the random data */
+long rdat(void) {
+	return random();
 }
 
 int main(int argc, char** argv) {
-	// set the seed to the number of seconds xor with nanoseconds
-	{
-		struct timespec ts;
-		clock_gettime(CLOCK_MONOTONIC, &ts);
-		srand((uint32_t)(ts.tv_nsec ^ ts.tv_sec)); // combine seconds and nanoseconds
-	}
+	// get the current time to set as the seed
+	struct timespec ts;
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	srandom(ts.tv_nsec);
 
-	// just print whether it's heads or tails
-	if (argc == 1) {
-		printf("%s\n", (rand() & 1) ? "heads" : "tails");
-		return 0;
-	}
+	// return the result if no input
+	if (argc <= 1) return printf("%s\n", (random() & 1) ? "heads" : "tails");
 
-	// if we have input; perform coin flips for those times
-	for (uint32_t i = 1; i < (unsigned)argc; ++i) {
-		int n = 0;           // contains the random data
-		uint64_t headsc = 0; // amount of heads
-		uint64_t tailsc = 0; // amount of tails
 
-		// get the integer from the string, return 1 if an error occurred
+	// loop through arguments
+	for (unsigned i = 1; i < (unsigned)argc; ++i) {
+		// parse the argument
 		errno = 0;
-		long const c = strtol(argv[i], NULL, 10);
-		if (errno == EINVAL) error("syntax error for string: %s\n", argv[i]);
-		if (c < 1 || c > (LONG_MAX - 1)) error("count may only be in between 1 and %l. Received %l\n", LONG_MAX, c);
+		ull c = strtoull(argv[i], NULL, 10);
+		if (errno != 0) error(errno, "parse error for string: '%s'\n", argv[i]);
+		if (c < 1 || c > (ULLONG_MAX - 1)) error(1, "count may only be in between 1 and %llu. Received %llu\n", ULLONG_MAX - 1, c);
 
 		// perform for the input count
-		for (long j = 0; j < c; ++j) {
-			if (n == 0) n = rand();                // get a new random number if the random data ran out
-			(void)((n & 1) ? headsc++ : tailsc++); // increment the correct counter
-			n >>= 1;                               // shift the random integer right by 1
+		ull headsc = 0; // amount of heads
+		ull tailsc = 0; // amount of tails
+
+
+		for (ull j = 0; j < c; ++j) {
+			ull n = rdat();
+
+#if defined(__GNUC__) && __GNUC__ >= 8
+# pragma GCC unroll 31
+#elif defined(__clang__)
+# pragma unroll 31
+#endif
+			for (ull b = 1; b <= INT32_MAX; b <<= 1)
+				(void)((n & b) ? headsc++ : tailsc++); // increment the correct counter
 		}
 
 		// print the results of this cycle
-		printf("results:\n heads: %lu\n tails: %lu\n", headsc, tailsc);
+		printf("results:\n heads: %llu\n tails: %llu\n", headsc, tailsc);
 	}
+	return 0;
 }
-#else
-# error "platform unsupported"
-#endif