varint: new file.

Move varint handling from tx.c and generalize it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Makefile

@@ -28,7 +28,8 @@ BITCOIN_SRC :=					\
 	bitcoin/script.c			\
 	bitcoin/shadouble.c			\
 	bitcoin/signature.c			\
-	bitcoin/tx.c
+	bitcoin/tx.c				\
+	bitcoin/varint.c
 BITCOIN_OBJS := $(BITCOIN_SRC:.c=.o)
 
 CORE_SRC :=					\
@@ -135,7 +136,8 @@ BITCOIN_HEADERS := bitcoin/address.h		\
 	bitcoin/script.h			\
 	bitcoin/shadouble.h			\
 	bitcoin/signature.h			\
-	bitcoin/tx.h
+	bitcoin/tx.h				\
+	bitcoin/varint.h
 
 CORE_HEADERS := close_tx.h			\
 	commit_tx.h				\

bitcoin/test/run-tx-encode.c

@@ -1,5 +1,6 @@
 #include "bitcoin/tx.c"
 #include "bitcoin/shadouble.c"
+#include "bitcoin/varint.c"
 #include <assert.h>
 #include <ccan/str/hex/hex.h>
 

bitcoin/tx.c

@@ -13,32 +13,9 @@
 static void add_varint(varint_t v,
 		       void (*add)(const void *, size_t, void *), void *addp)
 {
-	u8 buf[9], *p = buf;
-
-	if (v < 0xfd) {
-		*(p++) = v;
-	} else if (v <= 0xffff) {
-		(*p++) = 0xfd;
-		(*p++) = v;
-		(*p++) = v >> 8;
-	} else if (v <= 0xffffffff) {
-		(*p++) = 0xfe;
-		(*p++) = v;
-		(*p++) = v >> 8;
-		(*p++) = v >> 16;
-		(*p++) = v >> 24;
-	} else {
-		(*p++) = 0xff;
-		(*p++) = v;
-		(*p++) = v >> 8;
-		(*p++) = v >> 16;
-		(*p++) = v >> 24;
-		(*p++) = v >> 32;
-		(*p++) = v >> 40;
-		(*p++) = v >> 48;
-		(*p++) = v >> 56;
-	}
-	add(buf, p - buf, addp);
+	u8 buf[VARINT_MAX_LEN];
+
+	add(buf, varint_put(buf, v), addp);
 }
 
 static void add_le32(u32 v,
@@ -376,34 +353,15 @@ static const u8 *pull(const u8 **cursor, size_t *max, void *copy, size_t n)
 static u64 pull_varint(const u8 **cursor, size_t *max)
 {
 	u64 ret;
-	const u8 *p;
+	size_t len;
 
-	p = pull(cursor, max, NULL, 1);
-	if (!p)
+	len = varint_get(*cursor, *max, &ret);
+	if (len == 0) {
+		*cursor = NULL;
+		*max = 0;
 		return 0;
-
-	if (*p < 0xfd) {
-		ret = *p;
-	} else if (*p == 0xfd) {
-		p = pull(cursor, max, NULL, 2);
-		if (!p)
-			return 0;
-		ret = ((u64)p[1] << 8) + p[0];
-	} else if (*p == 0xfe) {
-		p = pull(cursor, max, NULL, 4);
-		if (!p)
-			return 0;
-		ret = ((u64)p[3] << 24) + ((u64)p[2] << 16)
-			+ ((u64)p[1] << 8) + p[0];
-	} else {
-		p = pull(cursor, max, NULL, 8);
-		if (!p)
-			return 0;
-		ret = ((u64)p[7] << 56) + ((u64)p[6] << 48)
-			+ ((u64)p[5] << 40) + ((u64)p[4] << 32)
-			+ ((u64)p[3] << 24) + ((u64)p[2] << 16)
-			+ ((u64)p[1] << 8) + p[0];
 	}
+	pull(cursor, max, NULL, len);
 	return ret;
 }
 

bitcoin/tx.h

@@ -3,12 +3,10 @@
 #include "config.h"
 #include "shadouble.h"
 #include "signature.h"
+#include "varint.h"
 #include <ccan/short_types/short_types.h>
 #include <ccan/tal/tal.h>
 
-/* We unpack varints for our in-memory representation */
-#define varint_t u64
-
 struct bitcoin_tx {
 	u32 version;
 	varint_t input_count;

bitcoin/varint.c

@@ -0,0 +1,62 @@
+#include "varint.h"
+
+size_t varint_put(u8 buf[VARINT_MAX_LEN], varint_t v)
+{
+	u8 *p = buf;
+
+	if (v < 0xfd) {
+		*(p++) = v;
+	} else if (v <= 0xffff) {
+		(*p++) = 0xfd;
+		(*p++) = v;
+		(*p++) = v >> 8;
+	} else if (v <= 0xffffffff) {
+		(*p++) = 0xfe;
+		(*p++) = v;
+		(*p++) = v >> 8;
+		(*p++) = v >> 16;
+		(*p++) = v >> 24;
+	} else {
+		(*p++) = 0xff;
+		(*p++) = v;
+		(*p++) = v >> 8;
+		(*p++) = v >> 16;
+		(*p++) = v >> 24;
+		(*p++) = v >> 32;
+		(*p++) = v >> 40;
+		(*p++) = v >> 48;
+		(*p++) = v >> 56;
+	}
+	return p - buf;
+}
+
+size_t varint_get(const u8 *p, size_t max, varint_t *val)
+{
+	if (max < 1)
+		return 0;
+
+	switch (*p) {
+	case 0xfd:
+		if (max < 3)
+			return 0;
+		*val = ((u64)p[1] << 8) + p[0];
+		return 3;
+	case 0xfe:
+		if (max < 5)
+			return 0;
+		*val = ((u64)p[3] << 24) + ((u64)p[2] << 16)
+			+ ((u64)p[1] << 8) + p[0];
+		return 5;
+	case 0xff:
+		if (max < 9)
+			return 0;
+		*val = ((u64)p[7] << 56) + ((u64)p[6] << 48)
+			+ ((u64)p[5] << 40) + ((u64)p[4] << 32)
+			+ ((u64)p[3] << 24) + ((u64)p[2] << 16)
+			+ ((u64)p[1] << 8) + p[0];
+		return 9;
+	default:
+		*val = *p;
+		return 1;
+	}
+}

bitcoin/varint.h

@@ -0,0 +1,17 @@
+#ifndef LIGHTNING_BITCOIN_VARINT_H
+#define LIGHTNING_BITCOIN_VARINT_H
+#include "config.h"
+#include <ccan/short_types/short_types.h>
+#include <stdlib.h>
+
+/* We unpack varints for our in-memory representation */
+#define varint_t u64
+
+#define VARINT_MAX_LEN 9
+
+/* Returns bytes used (up to 9) */
+size_t varint_put(u8 buf[VARINT_MAX_LEN], varint_t v);
+
+/* Returns bytes used: 0 if max_len too small. */
+size_t varint_get(const u8 *p, size_t max_len, varint_t *val);
+#endif /* LIGHTNING_BITCOIN_VARINT_H */