// SPDX-License-Identifier: MIT
/*
 * This file is based on klibc.
 */

#include <ctype.h>
#include <stddef.h>
#include <stdint.h>

static inline int digitval(int ch)
{
	if (ch >= '0' && ch <= '9') {
		return ch - '0';
	} else if (ch >= 'A' && ch <= 'Z') {
		return ch - 'A' + 10;
	} else if (ch >= 'a' && ch <= 'z') {
		return ch - 'a' + 10;
	} else {
		return -1;
	}
}

uintmax_t strntoumax(const char *nptr, char **endptr, int base, size_t n)
{
	int minus = 0;
	uintmax_t v = 0;
	int d;

	while (n && isspace((unsigned char)*nptr)) {
		nptr++;
		n--;
	}

	/* Single optional + or - */
	if (n) {
		char c = *nptr;
		if (c == '-' || c == '+') {
			minus = (c == '-');
			nptr++;
			n--;
		}
	}

	if (base == 0) {
		if (n >= 2 && nptr[0] == '0' &&
		    (nptr[1] == 'x' || nptr[1] == 'X')) {
			n -= 2;
			nptr += 2;
			base = 16;
		} else if (n >= 1 && nptr[0] == '0') {
			n--;
			nptr++;
			base = 8;
		} else {
			base = 10;
		}
	} else if (base == 16) {
		if (n >= 2 && nptr[0] == '0' &&
		    (nptr[1] == 'x' || nptr[1] == 'X')) {
			n -= 2;
			nptr += 2;
		}
	}

	while (n && (d = digitval(*nptr)) >= 0 && d < base) {
		v = v * base + d;
		n--;
		nptr++;
	}

	if (endptr)
		*endptr = (char *)nptr;

	return minus ? -v : v;
}
