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Add a runtime check to see if parse_int64 needs to workaround sscanf bugs. If that workaround is not needed parsing is nearly twice as fast.

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This commit is contained in:
Eric Haszlakiewicz
2013-02-09 17:35:33 -06:00
parent ca8b27d183
commit bfb329223a
1 changed files with 63 additions and 18 deletions
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81
json_util.c
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@@ -61,6 +61,10 @@
#include "json_tokener.h"
#include "json_util.h"
static int sscanf_is_broken = 0;
static int sscanf_is_broken_testdone = 0;
static void sscanf_is_broken_test(void);
struct json_object* json_object_from_file(const char *filename)
{
struct printbuf *pb;
@@ -142,41 +146,78 @@ int json_object_to_file(char *filename, struct json_object *obj)
return json_object_to_file_ext(filename, obj, JSON_C_TO_STRING_PLAIN);
}
/*
* Not all implementations of sscanf actually work properly.
* Check whether the one we're currently using does, and if
* it's broken, enable the workaround code.
*/
static void sscanf_is_broken_test()
{
int64_t num64;
(void)sscanf(" -01234567890123456789012345", "%" SCNd64, &num64);
int ret_errno = errno;
int is_int64_min = (num64 == INT64_MIN);
(void)sscanf(" 01234567890123456789012345", "%" SCNd64, &num64);
int ret_errno2 = errno;
int is_int64_max = (num64 == INT64_MAX);
if (ret_errno != ERANGE || !is_int64_min ||
ret_errno2 != ERANGE || !is_int64_max)
{
MC_DEBUG("sscanf_is_broken_test failed, enabling workaround code\n");
sscanf_is_broken = 1;
}
}
int json_parse_int64(const char *buf, int64_t *retval)
{
int64_t num64;
const char *buf_skip_space;
const char *buf_sig_digits;
int orig_has_neg;
int saved_errno;
if (!sscanf_is_broken_testdone)
{
sscanf_is_broken_test();
sscanf_is_broken_testdone = 1;
}
// Skip leading spaces
while (isspace((int)*buf) && *buf)
buf++;
errno = 0; // sscanf won't always set errno, so initialize
if (sscanf(buf, "%" SCNd64, &num64) != 1)
{
MC_DEBUG("Failed to parse, sscanf != 1\n");
return 1;
}
saved_errno = errno;
buf_skip_space = buf;
buf_sig_digits = buf;
orig_has_neg = 0;
// Skip leading spaces
while (isspace((int)*buf_skip_space) && *buf_skip_space)
buf_skip_space++;
if (*buf_skip_space == '-')
if (*buf_sig_digits == '-')
{
buf_skip_space++;
buf_sig_digits++;
orig_has_neg = 1;
}
// Skip leading zeros, but keep at least one digit
while (buf_skip_space[0] == '0' && buf_skip_space[1] != '\0')
buf_skip_space++;
if (buf_skip_space[0] == '0' && buf_skip_space[1] == '\0')
orig_has_neg = 0; // "-0" is the same as just plain "0"
if (saved_errno != ERANGE)
// Not all sscanf implementations actually work
if (sscanf_is_broken && saved_errno != ERANGE)
{
char buf_cmp[100];
char *buf_cmp_start = buf_cmp;
int recheck_has_neg = 0;
int buf_cmp_len;
// Skip leading zeros, but keep at least one digit
while (buf_sig_digits[0] == '0' && buf_sig_digits[1] != '\0')
buf_sig_digits++;
if (num64 == 0) // assume all sscanf impl's will parse -0 to 0
orig_has_neg = 0; // "-0" is the same as just plain "0"
snprintf(buf_cmp_start, sizeof(buf_cmp), "%" PRId64, num64);
if (*buf_cmp_start == '-')
{
@@ -190,18 +231,22 @@ int json_parse_int64(const char *buf, int64_t *retval)
* If the sign is different, or
* some of the digits are different, or
* there is another digit present in the original string
* then we NOT successfully parsed the value.
* then we have NOT successfully parsed the value.
*/
if (orig_has_neg != recheck_has_neg ||
strncmp(buf_skip_space, buf_cmp_start, strlen(buf_cmp_start)) != 0 ||
((int)strlen(buf_skip_space) != buf_cmp_len &&
isdigit((int)buf_skip_space[buf_cmp_len])
strncmp(buf_sig_digits, buf_cmp_start, strlen(buf_cmp_start)) != 0 ||
((int)strlen(buf_sig_digits) != buf_cmp_len &&
isdigit((int)buf_sig_digits[buf_cmp_len])
)
)
{
saved_errno = ERANGE;
}
}
// Not all sscanf impl's set the value properly when out of range.
// Always do this, even for properly functioning implementations,
// since it shouldn't slow things down much.
if (saved_errno == ERANGE)
{
if (orig_has_neg)