Fix promote rules for Mod (#162)

* Fix promote rules for `Mod`

* Fix a test

* Bump version

* Fix promotion with large integers, rework `is_prime`

Author: mtsch

Project.toml

@@ -1,7 +1,7 @@
 name = "Ripserer"
 uuid = "aa79e827-bd0b-42a8-9f10-2b302677a641"
 authors = ["mtsch <matijacufar@gmail.com>"]
-version = "0.16.11"
+version = "0.16.12"
 
 [deps]
 Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"

src/base/primefield.jl

@@ -4,7 +4,7 @@
 
 Return `true` if `n` is a prime number.
 """
-Base.@pure function is_prime(n::Int)
+function is_prime(n::Int)
     if iseven(n) || n < 2
         return n == 2
     else
@@ -81,6 +81,13 @@ Base.zero(::Type{Mod{M}}) where {M} = Mod{M}(0, false)
 Base.one(::Type{Mod{M}}) where {M} = Mod{M}(1, false)
 Base.sign(i::M) where {M<:Mod} = ifelse(iszero(i), zero(M), one(M))
 
-Base.promote_rule(::Type{Mod{M}}, ::Type{<:Integer}) where {M} = Mod{M}
+Base.promote_rule(::Type{Mod{M}}, ::Type{<:Mod}) where {M} = Union{}
+function Base.promote_rule(::Type{Mod{M}}, ::Type{I}) where {M,I<:Integer}
+    if Base.promote_type(I, Int128) === Int128 || Base.promote_type(I, Int128) === UInt128
+        return Mod{M}
+    else
+        return Union{}
+    end
+end
 
 Base.inv(i::Mod{M}) where {M} = Mod{M}(invmod(Int(i), M), false)

test/base/primefield.jl

@@ -53,7 +53,7 @@ end
         @test_throws ErrorException Mod{3}(1) < Mod{3}(2)
         @test_throws ErrorException Mod{3}(1) ≥ Mod{3}(2)
 
-        @test_throws StackOverflowError Mod{3}(1) + Mod{2}(1)
+        @test_throws ErrorException Mod{3}(1) + Mod{2}(1)
     end
 
     @testset "Printing" begin