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common: avoid locale dependent strtod(3)

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Replace `json_to_double()` (which uses `strtod(3)`) with our own
floating-point parsing function `json_to_millionths()` that
specifically expects to receive such a number that can fit in a
64 bit integer after being multiplied by 1 million.

The main piece of the code in this patch comes from
https://github.com/ElementsProject/lightning/pull/3535#discussion_r381041419

Changelog-None
This commit is contained in:
Rusty Russell
2020-02-19 11:11:36 +01:00
parent 89ceb273f5
commit 73ad9b5c0a
4 changed files with 104 additions and 11 deletions
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42
common/json.c
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@@ -13,8 +13,10 @@
#include <common/json.h>
#include <common/json_stream.h>
#include <common/node_id.h>
#include <common/overflows.h>
#include <common/utils.h>
#include <common/wireaddr.h>
#include <ctype.h>
#include <errno.h>
#include <inttypes.h>
#include <stdarg.h>
@@ -97,13 +99,45 @@ bool json_to_s64(const char *buffer, const jsmntok_t *tok, s64 *num)
return true;
}
bool json_to_double(const char *buffer, const jsmntok_t *tok, double *num)
bool json_to_millionths(const char *buffer, const jsmntok_t *tok,
u64 *millionths)
{
char *end;
int decimal_places = -1;
bool has_digits = 0;
*num = strtod(buffer + tok->start, &end);
if (end != buffer + tok->end)
*millionths = 0;
for (int i = tok->start; i < tok->end; i++) {
if (isdigit(buffer[i])) {
has_digits = true;
/* Ignore too much precision */
if (decimal_places >= 0 && ++decimal_places > 6)
continue;
if (mul_overflows_u64(*millionths, 10))
return false;
*millionths *= 10;
if (add_overflows_u64(*millionths, buffer[i] - '0'))
return false;
*millionths += buffer[i] - '0';
} else if (buffer[i] == '.') {
if (decimal_places != -1)
return false;
decimal_places = 0;
} else
return false;
}
if (!has_digits)
return false;
if (decimal_places == -1)
decimal_places = 0;
while (decimal_places < 6) {
if (mul_overflows_u64(*millionths, 10))
return false;
*millionths *= 10;
decimal_places++;
}
return true;
}