nostrdb: add supporting files for the bolt11 parser

A lot of this was pulled from core-lightning. Not sure what is actually
needed or not.

Signed-off-by: William Casarin <jb55@jb55.com>

nostrdb/bolt11/hash_u5.c

@@ -0,0 +1,48 @@
+#include "../config.h"
+#include "../endian.h"
+#include "hash_u5.h"
+#include <string.h>
+
+void hash_u5_init(struct hash_u5 *hu5, const char *hrp)
+{
+    hu5->buf = 0;
+    hu5->num_bits = 0;
+    sha256_init(&hu5->hash);
+    sha256_update(&hu5->hash, hrp, strlen(hrp));
+}
+
+void hash_u5(struct hash_u5 *hu5, const u8 *u5, size_t len)
+{
+    size_t bits = len * 5;
+
+    while (bits) {
+        size_t n = 5;
+
+        if (bits < n)
+            n = bits;
+
+        hu5->buf <<= n;
+        hu5->buf |= (*u5 >> (5-n));
+        bits -= n;
+        hu5->num_bits += n;
+
+        if (n == 5)
+            u5++;
+
+        if (hu5->num_bits >= 32) {
+            be32 be32 = cpu_to_be32((u32)(hu5->buf >> (hu5->num_bits-32)));
+            sha256_update(&hu5->hash, &be32, sizeof(be32));
+            hu5->num_bits -= 32;
+        }
+    }
+}
+
+void hash_u5_done(struct hash_u5 *hu5, struct sha256 *res)
+{
+    if (hu5->num_bits) {
+        be32 be32 = cpu_to_be32((u32)(hu5->buf << (32 - hu5->num_bits)));
+
+        sha256_update(&hu5->hash, &be32, (hu5->num_bits + 7) / 8);
+    }
+    sha256_done(&hu5->hash, res);
+}