Merge: Added contributing guidelines and link from readme

[nit.git] / lib / core / math.nit

diff --git a/lib/core/math.nit b/lib/core/math.nit
index bdd7daa..7b51e2a 100644 (file)
--- a/lib/core/math.nit
+++ b/lib/core/math.nit
@@ -128,7 +128,7 @@ redef class Int
        #
        # assert 3.is_prime
        # assert not 1.is_prime
-       # assert not 12.is_prime
+       # assert not 15.is_prime
        fun is_prime: Bool
        do
                if self == 2 then
@@ -136,7 +136,7 @@ redef class Int
                else if self <= 1 or self.is_even then
                        return false
                end
-               for i in [3..self.sqrt[ do
+               for i in [3..self.sqrt] do
                        if self % i == 0 then return false
                end
                return true
@@ -169,6 +169,16 @@ redef class Int
                end
                return res
        end
+
+       # Is `self` a power of two ?
+       #
+       # ~~~nit
+       # assert not 3.is_pow2
+       # assert 2.is_pow2
+       # assert 1.is_pow2
+       # assert not 0.is_pow2
+       # ~~~
+       fun is_pow2: Bool do return self != 0 and (self & self - 1) == 0
 end
 
 redef class Byte
@@ -524,11 +534,11 @@ redef class Sys
        end
 end
 
-# Computes the arc tangent given `x` and `y`.
+# Computes the arc tangent given `y` and `x`.
 #
 #     assert atan2(-0.0, 1.0) == -0.0
 #     assert atan2(0.0, 1.0) == 0.0
-fun atan2(x: Float, y: Float): Float `{ return atan2(x, y); `}
+fun atan2(y: Float, x: Float): Float `{ return atan2(y, x); `}
 
 # Approximate value of **pi**.
 fun pi: Float do return 3.14159265