_BitInt(N) defines an integer type with exactly N bits of precision. Both signed and unsigned variants are supported (unsigned _BitInt(N)). Bit-precise integer constants use the wb or uwb suffix. The maximum supported width is implementation-defined but at least BITINT_MAXWIDTH bits.

Standard integer types have implementation-defined sizes, requiring careful selection based on range requirements. Cryptographic algorithms, hardware interfaces, and arbitrary-precision arithmetic often need specific bit widths. _BitInt provides integers with exact precision, independent of the platform's native word sizes.

#include <stdio.h>

int main(void) {
    _BitInt(128) large = 12345678901234567890123456789012345wb;
    unsigned _BitInt(7) small = 100uwb;  // Fits in 7 bits (0-127)

    _BitInt(256) huge = large * 2;

    printf("small = %d\n", (int)small);
    printf("large fits in 128 bits\n");
}