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

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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.
This commit is contained in:
Willy Tarreau 2019-08-23 19:02:26 +02:00
parent 799e9ed62b
commit 4d589e719b
2 changed files with 41 additions and 0 deletions
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21
include/common/standard.h
View File

@ -201,6 +201,27 @@ static inline const char *LIM2A(unsigned long n, const char *alt)
return ret; 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 /* Encode the integer <i> into a varint (variable-length integer). The encoded
* value is copied in <*buf>. Here is the encoding format: * value is copied in <*buf>. Here is the encoding format:
* *

20
src/standard.c
View File

@ -4340,6 +4340,26 @@ int parse_dotted_uints(const char *str, unsigned int **nums, size_t *sz)
return 1; 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 */ /* do nothing, just a placeholder for debugging calls, the real one is in trace.c */
#ifndef USE_OBSOLETE_LINKER #ifndef USE_OBSOLETE_LINKER
__attribute__((weak,format(printf, 1, 2))) __attribute__((weak,format(printf, 1, 2)))