mpfr: speed improvements

Unlike GMP / BigInt, the MPFR library exposes an interface for external allocation:
http://www.mpfr.org/mpfr-current/mpfr.html#Custom-Interface

Using that allows us to use our fast memory-pool gc
and avoid adding finalizers and use the slow malloc/free functions.
(and in some cases, some of it might even end up on the stack!)

Also switch to allocating lgamma_sign on the stack, for better performance (and thread-safety)

Also fixes Serialization to preserve BigFloat precision.

Author: vtjnash

base/mpfr.jl

@@ -17,7 +17,7 @@ import
         cosh, sinh, tanh, sech, csch, coth, acosh, asinh, atanh,
         cbrt, typemax, typemin, unsafe_trunc, realmin, realmax, rounding,
         setrounding, maxintfloat, widen, significand, frexp, tryparse, iszero,
-        isone, big, RefValue
+        isone, big, _string_n
 
 import .Base.Rounding: rounding_raw, setrounding_raw
 
@@ -39,8 +39,8 @@ function __init__()
     nothing
 end
 
-const ROUNDING_MODE = RefValue{Cint}(0)
-const DEFAULT_PRECISION = RefValue(256)
+const ROUNDING_MODE = Ref{Cint}(0) # actually an Enum, defined by `to_mpfr`
+const DEFAULT_PRECISION = Ref{Int}(256)
 
 # Basic type and initialization definitions
 
@@ -54,21 +54,44 @@ mutable struct BigFloat <: AbstractFloat
     sign::Cint
     exp::Clong
     d::Ptr{Limb}
+    # _d::Buffer{Limb} # Julia gc handle for memory @ d
+    _d::String # Julia gc handle for memory @ d (optimized)
+
+    # Not recommended for general use:
+    # used internally by, e.g. deepcopy
+    global function _BigFloat(prec::Clong, sign::Cint, exp::Clong, d::String)
+        # ccall-based version, inlined below
+        #z = new(zero(Clong), zero(Cint), zero(Clong), C_NULL, d)
+        #ccall((:mpfr_custom_init,:libmpfr), Cvoid, (Ptr{Limb}, Clong), d, prec) # currently seems to be a no-op in mpfr
+        #NAN_KIND = Cint(0)
+        #ccall((:mpfr_custom_init_set,:libmpfr), Cvoid, (Ref{BigFloat}, Cint, Clong, Ptr{Limb}), z, NAN_KIND, prec, d)
+        #return z
+        return new(prec, sign, exp, pointer(d), d)
+    end
 
     function BigFloat()
-        prec = precision(BigFloat)
-        z = new(zero(Clong), zero(Cint), zero(Clong), C_NULL)
-        ccall((:mpfr_init2,:libmpfr), Cvoid, (Ref{BigFloat}, Clong), z, prec)
-        finalizer(cglobal((:mpfr_clear, :libmpfr)), z)
-        return z
+        prec::Clong = precision(BigFloat)
+        nb = ccall((:mpfr_custom_get_size,:libmpfr), Csize_t, (Clong,), prec)
+        nb = (nb + Core.sizeof(Limb) - 1) ÷ Core.sizeof(Limb) # align to number of Limb allocations required for this
+        #d = Vector{Limb}(undef, nb)
+        d = _string_n(nb * Core.sizeof(Limb))
+        EXP_NAN = Clong(1) - Clong(typemax(Culong) >> 1)
+        return _BigFloat(prec, one(Cint), EXP_NAN, d) # +NAN
     end
+end
 
-    # Not recommended for general use:
-    function BigFloat(prec::Clong, sign::Cint, exp::Clong, d::Ptr{Cvoid})
-        new(prec, sign, exp, d)
+# overload the definition of unsafe_convert to ensure that `x.d` is assigned
+# it may have been dropped in the event that the BigFloat was serialized
+Base.unsafe_convert(::Type{Ref{BigFloat}}, x::Ptr{BigFloat}) = x
+@inline function Base.unsafe_convert(::Type{Ref{BigFloat}}, x::Ref{BigFloat})
+    x = x[]
+    if x.d == C_NULL
+        x.d = pointer(x._d)
     end
+    return convert(Ptr{BigFloat}, Base.pointer_from_objref(x))
 end
 
+
 """
     BigFloat(x)
 
@@ -739,6 +762,7 @@ function setprecision(::Type{BigFloat}, precision::Int)
         throw(DomainError(precision, "`precision` cannot be less than 2."))
     end
     DEFAULT_PRECISION[] = precision
+    return precision
 end
 
 setprecision(precision::Int) = setprecision(BigFloat, precision)
@@ -957,11 +981,11 @@ set_emin!(x) = ccall((:mpfr_set_emin, :libmpfr), Cvoid, (Clong,), x)
 
 function Base.deepcopy_internal(x::BigFloat, stackdict::IdDict)
     haskey(stackdict, x) && return stackdict[x]
-    prec = precision(x)
-    y = BigFloat(zero(Clong), zero(Cint), zero(Clong), C_NULL)
-    ccall((:mpfr_init2,:libmpfr), Cvoid, (Ref{BigFloat}, Clong), y, prec)
-    finalizer(cglobal((:mpfr_clear, :libmpfr)), y)
-    ccall((:mpfr_set, :libmpfr), Int32, (Ref{BigFloat}, Ref{BigFloat}, Int32), y, x, ROUNDING_MODE[])
+    # d = copy(x._d)
+    d = x._d
+    d′ = GC.@preserve d unsafe_string(pointer(d), sizeof(d)) # creates a definitely-new String
+    y = _BigFloat(x.prec, x.sign, x.exp, d′)
+    #ccall((:mpfr_custom_move,:libmpfr), Cvoid, (Ref{BigFloat}, Ptr{Limb}), y, d) # unnecessary
     stackdict[x] = y
     return y
 end

stdlib/Serialization/src/Serialization.jl

@@ -313,11 +313,6 @@ function serialize(s::AbstractSerializer, n::BigInt)
     serialize(s, string(n, base = 62))
 end
 
-function serialize(s::AbstractSerializer, n::BigFloat)
-    serialize_type(s, BigFloat)
-    serialize(s, string(n))
-end
-
 function serialize(s::AbstractSerializer, ex::Expr)
     serialize_cycle(s, ex) && return
     l = length(ex.args)
@@ -1184,8 +1179,6 @@ function deserialize(s::AbstractSerializer, T::Type{Dict{K,V}}) where {K,V}
     return t
 end
 
-deserialize(s::AbstractSerializer, ::Type{BigFloat}) = parse(BigFloat, deserialize(s))
-
 deserialize(s::AbstractSerializer, ::Type{BigInt}) = parse(BigInt, deserialize(s), base = 62)
 
 function deserialize(s::AbstractSerializer, t::Type{Regex})

test/mpfr.jl

@@ -853,11 +853,17 @@ end
 @test_throws ArgumentError parse(BigFloat, "1\0")
 
 @testset "serialization (issue #12386)" begin
-    b = IOBuffer()
-    x = 2.1 * big(pi)
-    serialize(b, x)
-    seekstart(b)
-    @test deserialize(b) == x
+    b = PipeBuffer()
+    let x = setprecision(53) do
+            return 2.1 * big(pi)
+        end
+        serialize(b, x)
+        @test deserialize(b) == x
+    end
+    let x = BigFloat(Inf, 46)
+        serialize(b, x)
+        @test deserialize(b) == x == BigFloat(Inf, 2)
+    end
 end
 @test isnan(sqrt(BigFloat(NaN)))
 

test/precompile.jl

@@ -142,6 +142,9 @@ try
 
               g() = override(1.0)
               Test.@test g() === 2.0 # compile this
+
+              const abigfloat_f() = big"12.34"
+              const abigfloat_x = big"43.21"
           end
           """)
     @test_throws ErrorException Core.kwfunc(Base.nothing) # make sure `nothing` didn't have a kwfunc (which would invalidate the attempted test)
@@ -164,6 +167,10 @@ try
         @test Foo.override(1.0e0) == Float64('a')
         @test Foo.override(1.0f0) == 'b'
         @test Foo.override(UInt(1)) == 2
+
+        # Issue #15722
+        @test Foo.abigfloat_f()::BigFloat == big"12.34"
+        @test (Foo.abigfloat_x::BigFloat + 21) == big"64.21"
     end
 
     cachedir = joinpath(dir, "compiled", "v$(VERSION.major).$(VERSION.minor)")