fix rawbigints (JuliaLang#51122)

Using `Ptr` like that was incorrect. Among other issues, a `Ptr` doesn't
own the data it points to, so hold a `String` instead.

Fixes JuliaLang#51111

base/mpfr.jl

@@ -433,7 +433,7 @@ function to_ieee754(::Type{T}, x::BigFloat, rm) where {T<:AbstractFloat}
  ret_u = if is_regular & !rounds_to_inf & !rounds_to_zero
  if !exp_is_huge_p
  # significand
- v = RawBigInt(x.d, significand_limb_count(x))
+ v = RawBigInt{Limb}(x._d, significand_limb_count(x))
  len = max(ieee_precision + min(exp_diff, 0), 0)::Int
  signif = truncated(U, v, len) & significand_mask(T)
 

base/rawbigints.jl

@@ -5,15 +5,14 @@ Segment of raw words of bits interpreted as a big integer. Less
 significant words come first. Each word is in machine-native bit-order.
 """
 struct RawBigInt{T<:Unsigned}
- d::Ptr{T}
+ d::String
  word_count::Int
 
- function RawBigInt{T}(d::Ptr{T}, word_count::Int) where {T<:Unsigned}
+ function RawBigInt{T}(d::String, word_count::Int) where {T<:Unsigned}
  new{T}(d, word_count)
  end
 end
 
-RawBigInt(d::Ptr{T}, word_count::Int) where {T<:Unsigned} = RawBigInt{T}(d, word_count)
 elem_count(x::RawBigInt, ::Val{:words}) = x.word_count
 elem_count(x::Unsigned, ::Val{:bits}) = sizeof(x) * 8
 word_length(::RawBigInt{T}) where {T} = elem_count(zero(T), Val(:bits))
@@ -26,8 +25,10 @@ split_bit_index(x::RawBigInt, i::Int) = divrem(i, word_length(x), RoundToZero)
 `i` is the zero-based index of the wanted word in `x`, starting from
 the less significant words.
 """
-function get_elem(x::RawBigInt, i::Int, ::Val{:words}, ::Val{:ascending})
- unsafe_load(x.d, i + 1)
+function get_elem(x::RawBigInt{T}, i::Int, ::Val{:words}, ::Val{:ascending}) where {T}
+ # `i` must be nonnegative and less than `x.word_count`
+ d = x.d
+ (GC.@preserve d unsafe_load(Ptr{T}(pointer(d)), i + 1))::T
 end
 
 function get_elem(x, i::Int, v::Val, ::Val{:descending})

test/precompile.jl

@@ -244,6 +244,9 @@ precompile_test_harness(false) do dir
  const abigint_f() = big"123"
  const abigint_x = big"124"
 
+ # issue #51111
+ abigfloat_to_f32() = Float32(big"1.5")
+
  # issue #31488
  _v31488 = Base.StringVector(2)
  resize!(_v31488, 0)
@@ -299,6 +302,9 @@ precompile_test_harness(false) do dir
  @test Foo.abigint_f()::BigInt == big"123"
  @test Foo.abigint_x::BigInt + 1 == big"125"
 
+ # Issue #51111
+ @test Foo.abigfloat_to_f32() == 1.5f0
+
  @test Foo.x28297.result === missing
 
  @test Foo.d29936a === Dict