Merge pull request #38046 from JuliaLang/jb/spj/fixbigfloat

Fix some bugs with printf and BigFloat
JuliaLang · Oct 16, 2020 · 1dd89ec · 1dd89ec
2 parents 47d6067 + 91bafdf
commit 1dd89ec
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Showing 2 changed files with 31 additions and 6 deletions.
diff --git a/stdlib/Printf/src/Printf.jl b/stdlib/Printf/src/Printf.jl
@@ -379,16 +379,34 @@ tofloat(x) = Float64(x)
 tofloat(x::Base.IEEEFloat) = x
 tofloat(x::BigFloat) = x
 
+_snprintf(ptr, siz, str, arg) =
+    @ccall "libmpfr".mpfr_snprintf(ptr::Ptr{UInt8}, siz::Csize_t, str::Ptr{UInt8};
+                                   arg::Ref{BigFloat})::Cint
+
+const __BIG_FLOAT_MAX__ = 8192
+
 @inline function fmt(buf, pos, arg, spec::Spec{T}) where {T <: Floats}
     leftalign, plus, space, zero, hash, width, prec =
         spec.leftalign, spec.plus, spec.space, spec.zero, spec.hash, spec.width, spec.precision
     x = tofloat(arg)
-    if x isa BigFloat && isfinite(x)
-        ptr = pointer(buf, pos)
-        newpos = @ccall "libmpfr".mpfr_snprintf(ptr::Ptr{UInt8}, (length(buf) - pos + 1)::Csize_t, string(spec; modifier="R")::Ptr{UInt8}; arg::Ref{BigFloat})::Cint
-        newpos > 0 || error("invalid printf formatting for BigFloat")
-        return pos + newpos
-    elseif x isa BigFloat
+    if x isa BigFloat
+        if isfinite(x)
+            GC.@preserve buf begin
+                siz = length(buf) - pos + 1
+                str = string(spec; modifier="R")
+                len = _snprintf(pointer(buf, pos), siz, str, x)
+                if len > siz
+                    maxout = max(__BIG_FLOAT_MAX__,
+                                 ceil(Int, precision(x) * log(2) / log(10)) + 25)
+                    len > maxout &&
+                        error("Over $maxout bytes $len needed to output BigFloat $x")
+                    resize!(buf, len + 1)
+                    len = _snprintf(pointer(buf, pos), len + 1, str, x)
+                end
+                len > 0 || throw(ArgumentError("invalid printf formatting $str for BigFloat"))
+                return pos + len
+            end
+        end
         x = Float64(x)
     end
     if T == Val{'e'} || T == Val{'E'}

diff --git a/stdlib/Printf/test/runtests.jl b/stdlib/Printf/test/runtests.jl
@@ -411,6 +411,13 @@ end
     # Check bug with trailing nul printing BigFloat
     @test (Printf.@sprintf("%.330f", BigFloat(1)))[end] != '\0'
 
+    # Check bugs with truncated output printing BigFloat
+    @test (Printf.@sprintf("%f", parse(BigFloat, "1e400"))) ==
+           "10000000000000000000000000000000000000000000000000000000000000000000000000000025262527574416492004687051900140830217136998040684679611623086405387447100385714565637522507383770691831689647535911648520404034824470543643098638520633064715221151920028135130764414460468236314621044034960475540018328999334468948008954289495190631358190153259681118693204411689043999084305348398480210026863210192871358464.000000"
+
+    # Check that does not attempt to output incredibly large amounts of digits
+    @test_throws ErrorException Printf.@sprintf("%f", parse(BigFloat, "1e99999"))
+
     # issue #29662
     @test (Printf.@sprintf "%12.3e" pi*1e100) == "  3.142e+100"