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optimize length(::OrdinalRange) for large bit-ints #58864

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optimize length(::OrdinalRange) for large bit-ints #58864

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768e32e
optimize `length(::OrdinalRange)` for large bit-ints
mbauman Jul 1, 2025
e3e0389
remove max
mbauman Jul 1, 2025
62c3a44
make robust to non-bits steps
mbauman Jul 2, 2025
977cd9d
Merge remote-tracking branch 'origin/master' into mb+n5/ordinal-length
mbauman Jul 2, 2025
d0e1595
remove unneeded at-inline
mbauman Jul 2, 2025
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18 changes: 6 additions & 12 deletions base/range.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -802,21 +802,15 @@ let bigints = Union{Int, UInt, Int64, UInt64, Int128, UInt128},
# slightly more accurate length and checked_length in extreme cases
# (near typemax) for types with known `unsigned` functions
function length(r::OrdinalRange{T}) where T<:bigints
@inline
s = step(r)
diff = last(r) - first(r)
isempty(r) && return zero(diff)
# if |s| > 1, diff might have overflowed, but unsigned(diff)÷s should
# therefore still be valid (if the result is representable at all)
# n.b. !(s isa T)
if s isa Unsigned || -1 <= s <= 1 || s == -s
a = div(diff, s) % typeof(diff)
elseif s < 0
a = div(unsigned(-diff), -s) % typeof(diff)
else
a = div(unsigned(diff), s) % typeof(diff)
end
return a + oneunit(a)
# Compute `(diff ÷ s) + 1` in a manner robust to signed overflow
# by using the absolute values as unsigneds for non-empty ranges.
# Note that `s` may be a different type from T and diff; it may not
# even be a BitInteger that supports `unsigned`. Handle with care.
a = div(unsigned(flipsign(diff, s)), s) % typeof(diff)
return flipsign(a, s) + oneunit(a)
end
function checked_length(r::OrdinalRange{T}) where T<:bigints
s = step(r)
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2 changes: 2 additions & 0 deletions test/ranges.jl
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Expand Up @@ -743,6 +743,8 @@ end
@test length(typemin(T):typemax(T)) == T(0)
@test length(zero(T):one(T):typemax(T)) == typemin(T)
@test length(typemin(T):one(T):typemax(T)) == T(0)
@test length(StepRange{T,BigInt}(zero(T), 1, typemax(T))) == typemin(T)
@test length(StepRange{T,BigInt}(typemin(T), 1, typemax(T))) == T(0)
@test_throws OverflowError checked_length(zero(T):typemax(T))
@test_throws OverflowError checked_length(typemin(T):typemax(T))
@test_throws OverflowError checked_length(zero(T):one(T):typemax(T))
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