make use of scientific notation for BigFloat consistent with other ty…

…pes (#29211)

This switches to non-scientific notation when the scientific exponent
would be in `-4:5`, as is the case for e.g. Float64.
For example, `string(big(42.0))` is now `"42.0"`.

NEWS.md

@@ -53,6 +53,8 @@ Standard library changes
  returns a `BigFloat` with precision equal to `precision(BigFloat)` ([#29127]). The optional
  `precision` argument to override the global setting is now a keyword instead of positional
  argument ([#29157]).
+ * The use of scientific notation when printing `BigFloat` values is now consistent with other floating point
+ types ([#29211]).
  * `Regex` and `TimeZone` now behave like scalars when used in broadcasting ([#29913], [#30159]).
  * `Char` now behaves like a read-only 0-dimensional array ([#29819]).
  * `parse` now allows strings representing integer 0 and 1 for type `Bool` ([#29980]).

base/int.jl

@@ -589,7 +589,7 @@ julia> big"123_456"
 123456
 
 julia> big"7891.5"
-7.8915e+03
+7891.5
 ```
 """
 macro big_str(s)

base/math.jl

@@ -505,7 +505,7 @@ julia> sqrt(big(81))
 9.0
 
 julia> sqrt(big(-81))
-ERROR: DomainError with -8.1e+01:
+ERROR: DomainError with -81.0:
 NaN result for non-NaN input.
 Stacktrace:
  [1] sqrt(::BigFloat) at ./mpfr.jl:501

base/mpfr.jl

@@ -961,8 +961,20 @@ function _prettify_bigfloat(s::String)::String
  if endswith(mantissa, '.')
  mantissa = string(mantissa, '0')
  end
- if exponent == "+00"
- mantissa
+ expo = parse(Int, exponent)
+ if -5 < expo < 6
+ expo == 0 && return mantissa
+ int, frac = split(mantissa, '.')
+ if expo > 0
+ expo < length(frac) ?
+ string(int, frac[1:expo], '.', frac[expo+1:end]) :
+ string(int, frac, '0'^(expo-length(frac)), '.', '0')
+ else
+ neg = startswith(int, '-')
+ neg == true && (int = lstrip(int, '-'))
+ @assert length(int) == 1
+ string(neg ? '-' : "", '0', '.', '0'^(-expo-1), int, frac)
+ end
  else
  string(mantissa, 'e', exponent)
  end

base/number.jl

@@ -228,7 +228,7 @@ Multiply `x` and `y`, giving the result as a larger type.
 # Examples
 ```jldoctest
 julia> widemul(Float32(3.), 4.)
-1.2e+01
+12.0
 ```
 """
 widemul(x::Number, y::Number) = widen(x)*widen(y)

base/strings/io.jl

@@ -197,10 +197,10 @@ julia> repr(zeros(3))
 "[0.0, 0.0, 0.0]"
 
 julia> repr(big(1/3))
-"3.33333333333333314829616256247390992939472198486328125e-01"
+"0.333333333333333314829616256247390992939472198486328125"
 
 julia> repr(big(1/3), context=:compact => true)
-"3.33333e-01"
+"0.333333"
 
 ```
 """

test/mpfr.jl

@@ -653,15 +653,15 @@ end
  @test string(nextfloat(BigFloat(1))) == str
  end
  setprecision(21) do
- @test string(parse(BigFloat, "0.1")) == "1.0000002e-01"
+ @test string(parse(BigFloat, "0.1")) == "0.10000002"
  @test string(parse(BigFloat, "-9.9")) == "-9.9000015"
  end
  setprecision(40) do
- @test string(parse(BigFloat, "0.1")) == "1.0000000000002e-01"
+ @test string(parse(BigFloat, "0.1")) == "0.10000000000002"
  @test string(parse(BigFloat, "-9.9")) == "-9.8999999999942"
  end
  setprecision(123) do
- @test string(parse(BigFloat, "0.1")) == "9.99999999999999999999999999999999999953e-02"
+ @test string(parse(BigFloat, "0.1")) == "0.0999999999999999999999999999999999999953"
  @test string(parse(BigFloat, "-9.9")) == "-9.8999999999999999999999999999999999997"
  end
 end
@@ -941,6 +941,16 @@ end
  test_show_bigfloat(big"-1.23456789", contains_e=false, starts="-1.23")
  test_show_bigfloat(big"2.3457645687563543266576889678956787e10000", starts="2.345", ends="e+10000")
  test_show_bigfloat(big"-2.3457645687563543266576889678956787e-10000", starts="-2.345", ends="e-10000")
+ test_show_bigfloat(big"42.0", contains_e=false, starts="42.0")
+ test_show_bigfloat(big"420.0", contains_e=false, starts="420.0") # '0's have to be added on the right before point
+ test_show_bigfloat(big"-420.0", contains_e=false, starts="-420.0")
+ test_show_bigfloat(big"420000.0", contains_e=false, starts="420000.0")
+ test_show_bigfloat(big"654321.0", contains_e=false, starts="654321.0")
+ test_show_bigfloat(big"-654321.0", contains_e=false, starts="-654321.0")
+ test_show_bigfloat(big"6543210.0", contains_e=true, starts="6.5", ends="e+06")
+ test_show_bigfloat(big"0.000123", contains_e=false, starts="0.000123")
+ test_show_bigfloat(big"-0.000123", contains_e=false, starts="-0.000123")
+ test_show_bigfloat(big"0.00001234", contains_e=true, starts="1.23", ends="e-05")
 
  for to_string in [string,
  x->sprint(show, x),