// MulRange sets z to the product of all integers
// in the range [a, b] inclusively and returns z.
// If a > b (empty range), the result is 1.
func (z *Int) MulRange(a, b int64) *Int {
switch {
case a > b:
return z.SetInt64(1) // empty range
case a <= 0 && b >= 0:
return z.SetInt64(0) // range includes 0
}
// a <= b && (b < 0 || a > 0)
// Can use gmp factorial routine if a = 1 and b >= 1
if a == 1 && b >= 1 {
C.mpz_fac_ui(&z.i[0], C.ulong(b))
} else {
// Slow
z.SetInt64(a)
for i := a + 1; i <= b; i++ {
C.mpz_mul_si(&z.i[0], &z.i[0], C.long(i))
}
}
return z
}
// MulInt32 sets z to the product x*y and returns z.
//
// NB This is not part of big.Int
func (z *Int) MulInt32(x *Int, y int32) *Int {
x.doinit()
z.doinit()
C.mpz_mul_si(&z.i[0], &x.i[0], C.long(y))
return z
}