X-Git-Url: http://git.squeep.com/?p=reservoir_sample;a=blobdiff_plain;f=randomness.c;fp=randomness.c;h=90b375aec0a0f884c848fd8856771f5c05157cb1;hp=0000000000000000000000000000000000000000;hb=c0224807bccbd7e71e312fb4151378bff4f5a5db;hpb=4fccfc8fc60e56a5c09648e3914250f0312a0b5b

diff --git a/randomness.c b/randomness.c
new file mode 100644
index 0000000..90b375a
--- /dev/null
+++ b/randomness.c
@@ -0,0 +1,67 @@
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <time.h>
+#include <errno.h>
+#include <assert.h>
+
+#include "randomness.h"
+#include "notify.h"
+
+static int randomness_fd_ = -1;
+
+int randomness_init(const char *filename) {
+	if (filename != NULL) {
+		randomness_fd_ = open(filename, O_RDONLY);
+		if (randomness_fd_ == -1) {
+			NOTIFY_ERROR("%s('%s'):%s", "open", filename, strerror(errno));
+			return -1;
+		}
+		NOTIFY_DEBUG("reading randomness from '%s', fd:%d", filename, randomness_fd_);
+	} else {
+		if (randomness_fd_ != -1) {
+			close(randomness_fd_);
+			randomness_fd_ = -1;
+		}
+		srand48(time(NULL) ^ getpid());
+		NOTIFY_DEBUG("reading randomness from system PRNG");
+	}
+
+	return 0;
+}
+
+/*
+	Room for improvement: constrain bits of randomness consumed, based on #limit
+	Also maybe read chunks of randomness at a time
+ */
+unsigned long randomness_upto_inclusive(unsigned long limit) {
+	unsigned long randomness;
+
+	if (limit == 0)
+		return 0;
+
+	if (randomness_fd_ != -1) {
+		ssize_t len;
+
+		do {
+			len = read(randomness_fd_, &randomness, sizeof randomness);
+		} while (len == -1 && (errno == EINTR || errno == EAGAIN));
+		if (len == sizeof randomness) {
+			randomness %= limit + 1;
+			NOTIFY_DEBUG("randomness:%lu", randomness);
+			return randomness;
+		}
+		NOTIFY_ERROR("%s(%d, %zu):%zd:%s",
+		             "read", randomness_fd_, sizeof randomness, len,
+		             (len < 0) ? strerror(errno) : ( (len == 0) ? "EOF" : "not enough read" )
+		            );
+	}
+
+	/* fall back to pseudo-randomness if read failed */
+	randomness = mrand48();
+	randomness %= limit + 1;
+
+	NOTIFY_DEBUG("randomness:%lu", randomness);
+	return randomness;
+}
\ No newline at end of file