Skip to content

Fix gcdx and lcm with mixed signed/unsigned arguments #59628

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Sep 25, 2025
Merged

Fix gcdx and lcm with mixed signed/unsigned arguments #59628

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 12 additions & 0 deletions base/intfuncs.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -148,6 +148,8 @@ gcd(a::Rational) = checked_abs(a.num) // a.den
lcm(a::Union{Integer,Rational}) = gcd(a)
gcd(a::Unsigned, b::Signed) = gcd(promote(a, abs(b))...)
gcd(a::Signed, b::Unsigned) = gcd(promote(abs(a), b)...)
lcm(a::Unsigned, b::Signed) = lcm(promote(a, abs(b))...)
lcm(a::Signed, b::Unsigned) = lcm(promote(abs(a), b)...)
gcd(a::Real, b::Real) = gcd(promote(a,b)...)
lcm(a::Real, b::Real) = lcm(promote(a,b)...)
gcd(a::Real, b::Real, c::Real...) = gcd(a, gcd(b, c...))
Expand Down Expand Up @@ -252,6 +254,16 @@ function gcdx(a::Real, b::Real, cs::Real...)
d′, x, ys... = gcdx(d, cs...)
return d′, i*x, j*x, ys...
end
function gcdx(a::Signed, b::Unsigned)
R = promote_type(typeof(a), typeof(b))
_a = a % signed(R) # handle the case a == typemin(typeof(a)) if R != typeof(a)
d, u, v = gcdx(promote(abs(_a), b)...)
d, flipsign(u, a), v
end
function gcdx(a::Unsigned, b::Signed)
d, v, u = gcdx(b, a)
d, u, v
end

# multiplicative inverse of n mod m, error if none

Expand Down
29 changes: 29 additions & 0 deletions test/intfuncs.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,35 @@ end
x, y = Int8(-12), UInt(100)
d, u, v = gcdx(x, y)
@test x*u + y*v == d

end

# issue #58025
@testset "Mixed signed/unsigned types" begin
cases = [ # adapted from https://github.com/JuliaLang/julia/pull/59487#issuecomment-3258209203
(UInt16(100), Int8(-101)),
(Int8(-50), UInt16(75)),
(UInt32(12), Int16(-18)),
(Int64(-24), UInt8(36)),
(UInt8(15), Int16(-25)),
(Int32(-42), UInt64(56)),
(UInt128(1000), Int32(-1500)),
(UInt64(0), Int32(-5)),
(Int16(-7), UInt8(0)),
(Int8(-14), UInt8(13)),
]
for (a, b) in cases
g1 = gcd(a, b)
g2, s, t = gcdx(a, b)
@test g1 === g2
@test s*a + t*b == g2
@test g2 >= 0
@test lcm(a, b) === convert(typeof(g1), lcm(widen(a), widen(b)))
end

@test gcdx(Int16(-32768), Int8(-128)) === (Int16(128), Int16(0), Int16(-1))
@test gcdx(Int8(-128), UInt16(256)) === (0x0080, 0xffff, 0x0000)
@test_broken gcd(Int8(-128), UInt16(256)) === 0x0080
end

@testset "gcd/lcm/gcdx for custom types" begin
Expand Down