c: Implement the passgeny module.

This is the C implementation of the passgeny library.

c/passgeny/inc/passgeny.h

@@ -0,0 +1,56 @@
+#ifndef PASSGENY_H_INCLUDED
+#define PASSGENY_H_INCLUDED
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef struct passgeny passgeny_t;
+
+struct passgeny
+{
+    uint8_t     pg_master_hash[32];                 /* SHA256 of the master password */
+    char       *pg_pattern;                         /* Password pattern */
+    double      pg_last_bits_total;                 /* Total bits that were available for generating the last password */
+    double      pg_last_bits_used;                  /* Bits consumed when calculating the last password */
+};
+
+/*
+ * Initialize a new passgeny instance
+ *
+ * Note: The master password is hashed and remembered. The raw password is never
+ * stored in memory.
+ */
+bool passgeny_init(passgeny_t *passgeny, const char *master_password);
+
+/*
+ * Destroy a passgeny instance
+ */
+void passgeny_fini(passgeny_t *passgeny);
+
+/*
+ * Set the current pattern
+ */
+void passgeny_set_pattern(passgeny_t *passgeny, const char *pattern);
+
+/*
+ * Generate a new passgeny password using `domain`, `username` and optional
+ * tokens.
+ *
+ * The password is stored in the `out` string, where `out_sz` represents the
+ * maximum size of the string including '\0'
+ */
+bool passgeny_generate(
+        passgeny_t *passgeny,
+        char *out,
+        size_t out_sz,
+        const char *domain,
+        const char *username,
+        const char * const toknes[],
+        int ntokens);
+
+/*
+ * Dump some statistics
+ */
+void passgeny_dump_verbose(const passgeny_t *passgeny);
+
+#endif /* PASSGENY_H_INCLUDED */