countbits

commit e9ddd02b83bcad88950ba6d25ae9e1dc10e9c90d
Author: William Casarin <jb55@jb55.com>
Date:   Fri,  6 May 2022 08:24:54 -0700

countbits

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

Diffstat:
A
.gitignore
 | 
5
+++++
A
Makefile
 | 
4
++++
A
hex.h
 | 
69
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
main.c
 | 
119
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
proof.h
 | 
26
++++++++++++++++++++++++++

5 files changed, 223 insertions(+), 0 deletions(-)
diff --git a/.gitignore b/.gitignore
@@ -0,0 +1,5 @@
+.build-result
+.buildcmd
+countbits
+shell.nix
+.envrc
diff --git a/Makefile b/Makefile
@@ -0,0 +1,4 @@
+
+
+countbits: main.c
+	$(CC) $< -o $@
diff --git a/hex.h b/hex.h
@@ -0,0 +1,69 @@
+
+static inline int char_to_hex(unsigned char *val, char c)
+{
+	if (c >= '0' && c <= '9') {
+		*val = c - '0';
+		return 1;
+	}
+ 	if (c >= 'a' && c <= 'f') {
+		*val = c - 'a' + 10;
+		return 1;
+	}
+ 	if (c >= 'A' && c <= 'F') {
+		*val = c - 'A' + 10;
+		return 1;
+	}
+	return 0;
+}
+
+static inline int hex_decode(const char *str, size_t slen, void *buf, size_t bufsize)
+{
+	unsigned char v1, v2;
+	unsigned char *p = buf;
+
+	while (slen > 1) {
+		if (!char_to_hex(&v1, str[0]) || !char_to_hex(&v2, str[1]))
+			return 0;
+		if (!bufsize)
+			return 0;
+		*(p++) = (v1 << 4) | v2;
+		str += 2;
+		slen -= 2;
+		bufsize--;
+	}
+	return slen == 0 && bufsize == 0;
+}
+
+static inline size_t hex_str_size(size_t bytes)
+{
+	return 2 * bytes + 1;
+}
+
+static inline char hexchar(unsigned int val)
+{
+	if (val < 10)
+		return '0' + val;
+	if (val < 16)
+		return 'a' + val - 10;
+	abort();
+}
+
+static inline int hex_encode(const void *buf, size_t bufsize, char *dest, size_t destsize)
+{
+	size_t i;
+
+	if (destsize < hex_str_size(bufsize)) {
+		fprintf(stderr, "hexencode: destsize(%zu) < hex_str_size(%zu)\n", destsize, hex_str_size(bufsize));
+		return 0;
+	}
+
+	for (i = 0; i < bufsize; i++) {
+		unsigned int c = ((const unsigned char *)buf)[i];
+		*(dest++) = hexchar(c >> 4);
+		*(dest++) = hexchar(c & 0xF);
+	}
+	*dest = '\0';
+
+	return 1;
+}
+
diff --git a/main.c b/main.c
@@ -0,0 +1,119 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+static inline int char_to_hex(unsigned char *val, char c)
+{
+	if (c >= '0' && c <= '9') {
+		*val = c - '0';
+		return 1;
+	}
+ 	if (c >= 'a' && c <= 'f') {
+		*val = c - 'a' + 10;
+		return 1;
+	}
+ 	if (c >= 'A' && c <= 'F') {
+		*val = c - 'A' + 10;
+		return 1;
+	}
+	return 0;
+}
+
+static inline int hex_decode(const char *str, size_t slen, void *buf, size_t bufsize)
+{
+	unsigned char v1, v2;
+	unsigned char *p = buf;
+
+	while (slen > 1) {
+		if (!char_to_hex(&v1, str[0]) || !char_to_hex(&v2, str[1]))
+			return 0;
+		if (!bufsize)
+			return 0;
+		*(p++) = (v1 << 4) | v2;
+		str += 2;
+		slen -= 2;
+		bufsize--;
+	}
+	return slen == 0 && bufsize == 0;
+}
+
+static inline size_t hex_str_size(size_t bytes)
+{
+	return 2 * bytes + 1;
+}
+
+static inline char hexchar(unsigned int val)
+{
+	if (val < 10)
+		return '0' + val;
+	if (val < 16)
+		return 'a' + val - 10;
+	abort();
+}
+
+static inline int hex_encode(const void *buf, size_t bufsize, char *dest, size_t destsize)
+{
+	size_t i;
+
+	if (destsize < hex_str_size(bufsize)) {
+		fprintf(stderr, "hexencode: destsize(%zu) < hex_str_size(%zu)\n", destsize, hex_str_size(bufsize));
+		return 0;
+	}
+
+	for (i = 0; i < bufsize; i++) {
+		unsigned int c = ((const unsigned char *)buf)[i];
+		*(dest++) = hexchar(c >> 4);
+		*(dest++) = hexchar(c & 0xF);
+	}
+	*dest = '\0';
+
+	return 1;
+}
+
+
+static inline int zero_bits(unsigned char b)
+{
+	int n = 0;
+
+	if (b == 0)
+		return 8;
+
+	while (b >>= 1)
+		n++;
+
+	return 7-n;
+}
+
+/* find the number of leading zero bits in a hash */
+static int count_leading_zero_bits(unsigned char *hash, int len)
+{
+	int bits, total, i;
+
+	for (i = 0, total = 0; i < len; i++) {
+		bits = zero_bits(hash[i]);
+		total += bits;
+		if (bits != 8)
+			break;
+	}
+	return total;
+}
+
+int main(int argc, const char *argv[])
+{
+	unsigned char buf[4096];
+	const char *hex;
+	int bits, len;
+
+	if (argc < 1)
+		return 1;
+
+	hex = argv[1];
+	len = strlen(hex);
+
+	if (!hex_decode(hex, len, buf, len/2))
+		return 2;
+
+	bits = count_leading_zero_bits(buf, len / 2);
+	printf("%d\n", bits);
+	return 0;
+}
diff --git a/proof.h b/proof.h
@@ -0,0 +1,26 @@
+static inline int zero_bits(unsigned char b)
+{
+	int n = 0;
+
+	if (b == 0)
+		return 8;
+
+	while (b >>= 1)
+		n++;
+
+	return 7-n;
+}
+
+/* find the number of leading zero bits in a hash */
+static int count_leading_zero_bits(unsigned char *hash)
+{
+	int bits, total, i;
+
+	for (i = 0, total = 0; i < 32; i++) {
+		bits = zero_bits(hash[i]);
+		total += bits;
+		if (bits != 8)
+			break;
+	}
+	return total;
+}