From: Willy Tarreau <w@1wt.eu>
Date: Fri, 23 Aug 2019 17:02:26 +0000 (+0200)
Subject: MINOR: tools: add a function varint_bytes() to report the size of a varint
X-Git-Tag: v2.1-dev2~169
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4d589e719ba0f7c2421dbb98208de51c3e1cee1d;p=thirdparty%2Fhaproxy.git

MINOR: tools: add a function varint_bytes() to report the size of a varint

It will sometimes be useful to encode varints to know the output size in
advance. Two versions are provided, one inline using a switch/case construct
which will be trivial for use with constants (and will be very fast albeit
huge) and one function iterating on the number which is 5 times smaller,
for use with variables.
---

diff --git a/include/common/standard.h b/include/common/standard.h
index f0167d31aa..0b8a327266 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -201,6 +201,27 @@ static inline const char *LIM2A(unsigned long n, const char *alt)
 	return ret;
 }
 
+/* returns the number of bytes needed to encode <v> as a varint. Be careful, use
+ * it only with constants as it generates a large code (typ. 180 bytes). Use the
+ * varint_bytes() version instead in case of doubt.
+ */
+int varint_bytes(uint64_t v);
+static inline int __varint_bytes(uint64_t v)
+{
+	switch (v) {
+	case 0x0000000000000000 ... 0x00000000000000ef: return 1;
+	case 0x00000000000000f0 ... 0x00000000000008ef: return 2;
+	case 0x00000000000008f0 ... 0x00000000000408ef: return 3;
+	case 0x00000000000408f0 ... 0x00000000020408ef: return 4;
+	case 0x00000000020408f0 ... 0x00000001020408ef: return 5;
+	case 0x00000001020408f0 ... 0x00000081020408ef: return 6;
+	case 0x00000081020408f0 ... 0x00004081020408ef: return 7;
+	case 0x00004081020408f0 ... 0x00204081020408ef: return 8;
+	case 0x00204081020408f0 ... 0x10204081020408ef: return 9;
+	default: return 10;
+	}
+}
+
 /* Encode the integer <i> into a varint (variable-length integer). The encoded
  * value is copied in <*buf>. Here is the encoding format:
  *
diff --git a/src/standard.c b/src/standard.c
index 717c14a946..08a2c0d46e 100644
--- a/src/standard.c
+++ b/src/standard.c
@@ -4340,6 +4340,26 @@ int parse_dotted_uints(const char *str, unsigned int **nums, size_t *sz)
 	return 1;
 }
 
+
+/* returns the number of bytes needed to encode <v> as a varint. An inline
+ * version exists for use with constants (__varint_bytes()).
+ */
+int varint_bytes(uint64_t v)
+{
+	int len = 1;
+
+	if (v >= 240) {
+		v = (v - 240) >> 4;
+		while (1) {
+			len++;
+			if (v < 128)
+				break;
+			v = (v - 128) >> 7;
+		}
+	}
+	return len;
+}
+
 /* do nothing, just a placeholder for debugging calls, the real one is in trace.c */
 #ifndef USE_OBSOLETE_LINKER
 __attribute__((weak,format(printf, 1, 2)))