allow taking inverses mod 1

pwl · Nov 15, 2013 · 0cad721 · 0cad721
1 parent 6a2141e
commit 0cad721
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Showing 3 changed files with 6 additions and 3 deletions.
diff --git a/base/gmp.jl b/base/gmp.jl
@@ -167,7 +167,10 @@ end
 function invmod(x::BigInt, y::BigInt)
  z = BigInt()
  y = abs(y)
- if (y<2 || ccall((:__gmpz_invert, :libgmp), Cint, (Ptr{BigInt}, Ptr{BigInt}, Ptr{BigInt}), &z, &x, &y) == 0)
+ if y == 1
+ return big(0)
+ end
+ if (y==0 || ccall((:__gmpz_invert, :libgmp), Cint, (Ptr{BigInt}, Ptr{BigInt}, Ptr{BigInt}), &z, &x, &y) == 0)
  error("no inverse exists")
  end
  return z

diff --git a/base/intfuncs.jl b/base/intfuncs.jl
@@ -68,7 +68,7 @@ gcdx(a::Integer, b::Integer) = gcdx(promote(a,b)...)
 # multiplicative inverse of n mod m, error if none
 function invmod(n, m)
  g, x, y = gcdx(n, m)
- if g != 1 || m == 0 || m == 1 || m == -1
+ if g != 1 || m == 0
  error("no inverse exists")
  end
  x < 0 ? abs(m) + x : x

diff --git a/test/numbers.jl b/test/numbers.jl
@@ -1522,7 +1522,7 @@ for i = -20:20, j = -20:20
  @test d == gcd(ib,jb)
  @test lcm(i,j) == lcm(ib,jb)
  @test gcdx(i,j) == gcdx(ib,jb)
- if abs(j) < 2
+ if j == 0
  @test_throws invmod(i,j)
  @test_throws invmod(ib,jb)
  elseif d == 1