Description
Here is a pretty self explanatory MWE:
julia> prevpow(2, 5.1)
4
julia> prevpow(2, BigFloat(5.1))
ERROR: MethodError: no method matching typemax(::Type{BigInt})
The function `typemax` exists, but no method is defined for this combination of argument types.
Closest candidates are:
typemax(::Type{LibGit2.Consts.GIT_SUBMODULE_IGNORE})
@ LibGit2 Enums.jl:217
typemax(::Type{LibGit2.Consts.GIT_MERGE_FILE_FAVOR})
@ LibGit2 Enums.jl:217
typemax(::Type{Int128})
@ Base int.jl:823
...
Stacktrace:
[1] typemax(x::BigInt)
@ Base ./float.jl:1039
[2] prevpow(a::Int64, x::BigFloat)
@ Base ./intfuncs.jl:570
[3] top-level scope
@ REPL[12]:1
julia> prevpow(BigFloat(2), 5.1)
4.0
julia> prevpow(BigInt(2), 5.1)
ERROR: MethodError: no method matching typemax(::Type{BigInt})
The function `typemax` exists, but no method is defined for this combination of argument types.
Closest candidates are:
typemax(::Type{LibGit2.Consts.GIT_SUBMODULE_IGNORE})
@ LibGit2 Enums.jl:217
typemax(::Type{LibGit2.Consts.GIT_MERGE_FILE_FAVOR})
@ LibGit2 Enums.jl:217
typemax(::Type{Int128})
@ Base int.jl:823
...
Stacktrace:
[1] typemax(x::BigInt)
@ Base ./float.jl:1039
[2] prevpow(a::BigInt, x::Float64)
@ Base ./intfuncs.jl:570
[3] top-level scope
@ REPL[14]:1
julia> versioninfo()
Julia Version 1.11.4
Commit 8561cc3d68d (2025-03-10 11:36 UTC)
Build Info:
Official https://julialang.org/ release
Platform Info:
OS: macOS (arm64-apple-darwin24.0.0)
CPU: 10 × Apple M1 Pro
WORD_SIZE: 64
LLVM: libLLVM-16.0.6 (ORCJIT, apple-m1)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)
Environment:
JULIA_EDITOR = code
JULIA_NUM_THREADS =
The error is coming from a typemax call in the prevpow code.
As far as fixing it goes, adding (x isa BigInt) || ... pushes the problem downstream, where mul_with_overflow isn't defined for a mixture of Int and BigInt, this approach would require changing that line to mul_with_overflow(promote(a,p)...) I do not know if this fits the style, or if it is performant.
First and foremost I think there needs to be more test cases to catch things like this, here is the summary of combinations I have right now, with coverage of the special case a == 2
@testset "prevpow input types" begin
@test prevpow(3,7) == 3
@test prevpow(3, BigInt(7)) == 3 broken = true
@test prevpow(3, BigFloat(7)) == 3 broken = true
@test prevpow(BigInt(3), 7) ==3 broken = true
@test prevpow(BigInt(3), BigInt(7)) == 3 broken = true
@test prevpow(BigInt(3), BigFloat(7)) == 3 broken = true
@test prevpow(BigFloat(3), 7) == 3
@test prevpow(BigFloat(3), BigInt(7)) == 3
@test prevpow(BigFloat(3), BigFloat(7)) == 3
@test prevpow(BigInt(2), 7) == 4
@test prevpow(BigInt(2), BigInt(7)) == 4
@test prevpow(BigFloat(2), 7) == 4
@test prevpow(2, BigInt(7)) == 4
@test prevpow(2, BigFloat(7)) == 4 broken = true
end