in src/detail/encode_integer.cpp [104:122]
void encode_positive_integer_32(encode_context &context, uint32_t value) {
#define ENCODE(bits, digits) do { \
using type = uint_fast ## bits ## _t; \
return positive<type, digits>::encode(context, type(value)); \
} while (false)
#define CUTOFF(bits, digits, cutoff) if (value < cutoff ## UL) ENCODE(bits, digits);
CUTOFF(32, 1, 10);
CUTOFF(32, 2, 100);
CUTOFF(32, 3, 1000);
CUTOFF(32, 4, 10000);
CUTOFF(32, 5, 100000);
CUTOFF(32, 6, 1000000);
CUTOFF(32, 7, 10000000);
CUTOFF(32, 8, 100000000);
CUTOFF(32, 9, 1000000000);
ENCODE(32, 10);
#undef CUTOFF
#undef ENCODE
}