#ifndef R_TYPES_OVERFLOW_H
#define R_TYPES_OVERFLOW_H

#ifdef __cplusplus
extern "C" {
#endif

// TODO: Use CLANG/GCC builtins if available: __builtin_mul_overflow
// https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

// ADD
// if ((x > 0) && (a > INT_MAX - x)) /* `a + x` would overflow */;
// if ((x < 0) && (a < INT_MIN - x)) /* `a + x` would underflow */;
#define SZT_ADD_OVFCHK(x,y) ((SIZE_MAX - (x)) < (y))
#define SSZT_ADD_OVFCHK(a,x) ((((x) > 0) && ((a) > SSIZE_MAX - (x))) || (((x) < 0) && ((a) < SSIZE_MIN - (x))))
#define UT64_ADD_OVFCHK(x,y) ((UT64_MAX - (x)) < (y))
#define ST64_ADD_OVFCHK(a,x) ((((x) > 0) && ((a) > ST64_MAX - (x))) || (((x) < 0) && ((a) < ST64_MIN - (x))))
#define UT32_ADD_OVFCHK(x,y) ((UT32_MAX - (x)) < (y))
#define ST32_ADD_OVFCHK(a,x) ((((x) > 0) && ((a) > ST32_MAX - (x))) || (((x) < 0) && ((a) < ST32_MIN - (x))))
#define UT16_ADD_OVFCHK(x,y) (((y) > 0x8000) || ((UT16_MAX - (x)) < (y)))
#define ST16_ADD_OVFCHK(a,b) ((((b) > 0) && ((a) > ST16_MAX - (b))) || (((b) < 0) && ((a) < ST16_MIN - (b))))
#define UT8_ADD_OVFCHK(x,y) ((UT8_MAX - (x)) < (y))
#define ST8_ADD_OVFCHK(a,x) ((((x) > 0) && ((a) > ST8_MAX - (x))) || (((x) < 0) && ((a) < ST8_MIN - (x))))

// SUB
// if ((x < 0) && (a > INT_MAX + x)) /* `a - x` would overflow */;
// if ((x > 0) && (a < INT_MIN + x)) /* `a - x` would underflow */;
#define SZT_SUB_OVFCHK(a,b) SZT_ADD_OVFCHK(a,-(b))
#define SSZT_SUB_OVFCHK(a,b) SSZT_ADD_OVFCHK(a,-(b))
#define UT64_SUB_OVFCHK(a,b) UT64_ADD_OVFCHK(a,-(b))
#define ST64_SUB_OVFCHK(a,b) ST64_ADD_OVFCHK(a,-(b))
#define UT32_SUB_OVFCHK(a,b) UT32_ADD_OVFCHK(a,-(b))
#define ST32_SUB_OVFCHK(a,b) ST32_ADD_OVFCHK(a,-(b))
#define UT16_SUB_OVFCHK(a,b) ((a) < (b))
#define ST16_SUB_OVFCHK(a,b) ST16_ADD_OVFCHK(a,-(b))
#define UT8_SUB_OVFCHK(a,b) UT8_ADD_OVFCHK(a,-(b))
#define ST8_SUB_OVFCHK(a,b) ST8_ADD_OVFCHK(a,-(b))

// MUL
#define UNSIGNED_MUL_OVERFLOW_CHECK(overflow_name, type_base, type_min, type_max) \
static inline bool overflow_name(type_base a, type_base b) { \
	return (a > 0 && b > 0 && a > type_max / b); \
}

#define SIGNED_MUL_OVERFLOW_CHECK(overflow_name, type_base, type_min, type_max) \
static inline bool overflow_name(type_base a, type_base b) { \
	if (a > 0) { \
		if (b > 0) { return a > type_max / b; } \
		return b < type_min / a; \
	} \
	if (b > 0) { return a < type_min / b; } \
	return a && b < type_max / a; \
}

#define SIGNED_DIV_OVERFLOW_CHECK(overflow_name, type_base, type_mid, type_max) \
static inline bool overflow_name(type_base a, type_base b) { \
	return (!b || (a == type_mid && b == type_max)); \
}
#define UNSIGNED_DIV_OVERFLOW_CHECK(overflow_name, type_base, type_min, type_max) \
static inline bool overflow_name(type_base a, type_base b) { \
	(void)(a); \
	return !b; \
}

SIGNED_DIV_OVERFLOW_CHECK(ST8_DIV_OVFCHK,  ut8,  UT8_GT0,  UT8_MAX)
SIGNED_DIV_OVERFLOW_CHECK(ST16_DIV_OVFCHK, ut16, UT16_GT0, UT16_MAX)
SIGNED_DIV_OVERFLOW_CHECK(ST32_DIV_OVFCHK, ut32, UT32_GT0, UT32_MAX)
SIGNED_DIV_OVERFLOW_CHECK(ST64_DIV_OVFCHK, ut64, UT64_GT0, UT64_MAX)
UNSIGNED_DIV_OVERFLOW_CHECK(UT8_DIV_OVFCHK,  ut8,  UT8_MIN,  UT8_MAX)
UNSIGNED_DIV_OVERFLOW_CHECK(UT16_DIV_OVFCHK, ut16, UT16_MIN, UT16_MAX)
UNSIGNED_DIV_OVERFLOW_CHECK(UT32_DIV_OVFCHK, ut32, UT32_MIN, UT32_MAX)
UNSIGNED_DIV_OVERFLOW_CHECK(UT64_DIV_OVFCHK, ut64, UT64_MIN, UT64_MAX)
// TODO: Windows doesn't have ssize_t, and we don't need this check yet
// SIGNED_MUL_OVERFLOW_CHECK(SSZT_MUL_OVFCHK, ssize_t, SSZT_MIN, SSZT_MAX)
SIGNED_MUL_OVERFLOW_CHECK(ST8_MUL_OVFCHK, st8, ST8_MIN, ST8_MAX)
SIGNED_MUL_OVERFLOW_CHECK(ST16_MUL_OVFCHK, st16, ST16_MIN, ST16_MAX)
SIGNED_MUL_OVERFLOW_CHECK(ST32_MUL_OVFCHK, st32, ST32_MIN, ST32_MAX)
SIGNED_MUL_OVERFLOW_CHECK(ST64_MUL_OVFCHK, st64, ST64_MIN, ST64_MAX)
UNSIGNED_MUL_OVERFLOW_CHECK(SZT_MUL_OVFCHK, size_t, SZT_MIN, SZT_MAX)
UNSIGNED_MUL_OVERFLOW_CHECK(UT8_MUL_OVFCHK, ut8, UT8_MIN, UT8_MAX)
UNSIGNED_MUL_OVERFLOW_CHECK(UT16_MUL_OVFCHK, ut16, UT16_MIN, UT16_MAX)
UNSIGNED_MUL_OVERFLOW_CHECK(UT32_MUL_OVFCHK, ut32, UT32_MIN, UT32_MAX)
UNSIGNED_MUL_OVERFLOW_CHECK(UT64_MUL_OVFCHK, ut64, UT64_MIN, UT64_MAX)

#ifdef __cplusplus
}
#endif

#endif
