Improve calculation of JSON_INT_MAX

[trevnorris]

From https://github.com/udp/json-parser/blob/e6426ae/json.c#L49-L55. That value can be calculated mathematically using 2**((n * 8) - 1) - 1. Which can also be done using the following bit shift:

static const json_int_t JSON_INT_MAX = (1L << ((8 * sizeof(json_int_t) - 1))) - 1

[harkue]

If Using

static const json_int_t JSON_INT_MAX = (1L << ((8 * sizeof(json_int_t) - 1))) - 1

It will trigger a warining such as:

json.c:48:1: warning: integer overflow in expression [-Woverflow]
 static const json_int_t JSON_INT_MAX = (1L << ((8 * sizeof(json_int_t) - 1))) - 1;
 ^~~~~~

[harkue]

Using this will be better:

static const json_int_t JSON_INT_MAX = (json_int_t)((1UL<<((sizeof(json_int_t) * 8) - 1)) - 1);

[LB--]

Looks like this is being addressed in #102

[DimitriPapadopoulos]

Would that work on a platform where long (and hence 1UL) is 32-bit, while json_int_t is defined (probably not in a portable way) to be 64-bit?

[DimitriPapadopoulos]

What was wrong with the previous definition of JSON_INT_MAX reverted by fcfa748? It's not clear to me.

static const json_int_t JSON_INT_MAX = (((unsigned json_int_t)0 - (unsigned json_int_t)1) / (unsigned json_int_t)2);

Perhaps casting back to signed?

static const json_int_t JSON_INT_MAX = (json_int_t)(((unsigned json_int_t)0 - (unsigned json_int_t)1) / (unsigned json_int_t)2);