bugfix for lcm(0,0), add test coverage of gcd-related functions

base/intfuncs.jl

@@ -40,7 +40,9 @@ function gcd{T<:Integer}(a::T, b::T)
     end
     abs(a)
 end
-lcm{T<:Integer}(a::T, b::T) = abs(a * div(b, gcd(b,a)))
+
+# explicit a==0 test is to handle case of lcm(0,0) correctly
+lcm{T<:Integer}(a::T, b::T) = a == 0 ? a : abs(a * div(b, gcd(b,a)))
 
 gcd(a::Integer) = a
 lcm(a::Integer) = a

doc/helpdb.jl

@@ -3885,13 +3885,13 @@ popdisplay(d::Display)
 
 ("Mathematical Functions","Base","gcd","gcd(x, y)
 
-   Greatest common (positive) divisor
+   Greatest common (positive) divisor (or zero if x and y are both zero).
 
 "),
 
 ("Mathematical Functions","Base","lcm","lcm(x, y)
 
-   Least common (positive) multiple
+   Least common (non-negative) multiple.
 
 "),
 

doc/stdlib/base.rst

@@ -2632,11 +2632,11 @@ Mathematical Functions
 
 .. function:: gcd(x,y)
 
-   Greatest common (positive) divisor.
+   Greatest common (positive) divisor (or zero if x and y are both zero).
 
 .. function:: lcm(x,y)
 
-   Least common (positive) multiple.
+   Least common (non-negative) multiple.
 
 .. function:: gcdx(x,y)
 

test/numbers.jl

@@ -1511,3 +1511,16 @@ end
 # overflow in rational comparison
 @test 3//2 < typemax(Int)
 @test 3//2 <= typemax(Int)
+
+# check gcd and related functions against GMP
+for i = -20:20, j = -20:20
+    local d = gcd(i,j)
+    @test d >= 0
+    @test lcm(i,j) >= 0
+    local ib = big(i)
+    local jb = big(j)
+    @test d == gcd(ib,jb)
+    @test lcm(i,j) == lcm(ib,jb)
+    @test gcdx(i,j) == gcdx(ib,jb)
+    @test d != 1 || invmod(i,j) == invmod(ib,jb)
+end