binomial(::BigInt, k) should give BigInt(0) for k < 0

jiahao · Jan 5, 2015 · b5bd61d · b5bd61d
1 parent 7d4c3a5
commit b5bd61d
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diff --git a/base/gmp.jl b/base/gmp.jl
@@ -436,7 +436,7 @@ function binomial(n::BigInt, k::UInt)
  ccall((:__gmpz_bin_ui, :libgmp), Void, (Ptr{BigInt}, Ptr{BigInt}, Culong), &z, &n, k)
  return z
 end
-binomial(n::BigInt, k::Integer) = k < 0 ? throw(DomainError()) : binomial(n, uint(k))
+binomial(n::BigInt, k::Integer) = k < 0 ? BigInt(0) : binomial(n, uint(k))
 
 ==(x::BigInt, y::BigInt) = cmp(x,y) == 0
 ==(x::BigInt, i::Integer) = cmp(x,i) == 0

diff --git a/test/bigint.jl b/test/bigint.jl
@@ -164,6 +164,7 @@ end
 @test lcm(BigInt(48), BigInt(180)) == 720
 
 @test factorial(BigInt(40)) == BigInt("815915283247897734345611269596115894272000000000")
+@test binomial(BigInt(1), -1) == BigInt(0)
 @test binomial(BigInt(-53), 42) == BigInt("959509335087854414441273718")
 @test binomial(BigInt(113), BigInt(42)) == BigInt("18672199984318438125634054194360")