Make ranges more robust with unsigned indexes.

Author: gbaraldi

base/range.jl

@@ -963,14 +963,24 @@ end
 # This is separate to make it useful even when running with --check-bounds=yes
 function unsafe_getindex(r::StepRangeLen{T}, i::Integer) where T
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    u = i - r.offset
-    T(r.ref + u*r.step)
+    if i < r.offset # 1 <= offset <= len && 1 <= i <= len
+        u = r.offset - i
+        return T(r.ref - u*r.step)
+    else
+        u = i - r.offset
+        return T(r.ref + u*r.step)
+    end
 end
 
 function _getindex_hiprec(r::StepRangeLen, i::Integer)  # without rounding by T
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    u = i - r.offset
-    r.ref + u*r.step
+    if i < r.offset # 1 <= offset <= len && 1 <= i <= len
+        u = r.offset - i
+        return r.ref - u*r.step
+    else
+        u = i - r.offset
+        return r.ref + u*r.step
+    end
 end
 
 function unsafe_getindex(r::LinRange, i::Integer)

base/twiceprecision.jl

@@ -478,15 +478,23 @@ function unsafe_getindex(r::StepRangeLen{T,<:TwicePrecision,<:TwicePrecision}, i
     # Very similar to _getindex_hiprec, but optimized to avoid a 2nd call to add12
     @inline
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    u = i - r.offset
+    if i < r.offset # 1 <= offset <= len && 1 <= i <= len
+        u = r.offset - i
+    else
+        u = i - r.offset
+    end
     shift_hi, shift_lo = u*r.step.hi, u*r.step.lo
     x_hi, x_lo = add12(r.ref.hi, shift_hi)
     T(x_hi + (x_lo + (shift_lo + r.ref.lo)))
 end
 
 function _getindex_hiprec(r::StepRangeLen{<:Any,<:TwicePrecision,<:TwicePrecision}, i::Integer)
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    u = i - r.offset
+    if i < r.offset # 1 <= offset <= len && 1 <= i <= len
+        u = r.offset - i
+    else
+        u = i - r.offset
+    end
     shift_hi, shift_lo = u*r.step.hi, u*r.step.lo
     x_hi, x_lo = add12(r.ref.hi, shift_hi)
     x_hi, x_lo = add12(x_hi, x_lo + (shift_lo + r.ref.lo))

test/ranges.jl

@@ -2528,3 +2528,8 @@ end
     end
 
 end
+
+@testset "unsigned index #44895" begin
+    x = range(-1,1,length=11)
+    x[UInt(1)] == 1.0
+end