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 f0167d3..0b8a327 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -201,6 +201,27 @@
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 717c14a..08a2c0d 100644
--- a/src/standard.c
+++ b/src/standard.c
@@ -4340,6 +4340,26 @@
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)))