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Fix strformat neg zero #7954

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merged 5 commits into from
Jun 5, 2018
Merged

Fix strformat neg zero #7954

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0e8a4ba
fix strformat handling of neg zero with sign
skilchen May 31, 2018
9caefe1
better tests for neg zero with sign
skilchen May 31, 2018
be51fb4
rebase on latest devel
skilchen Jun 4, 2018
5f274cc
Merge branch 'devel' of https://github.com/nim-lang/nim into fix_strf…
skilchen Jun 4, 2018
a2a2528
use inplace insertion of the sign as suggested by Varriount
skilchen Jun 5, 2018
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7 changes: 6 additions & 1 deletion lib/pure/strformat.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -527,8 +527,13 @@ proc format*(value: SomeFloat; specifier: string; res: var string) =
var sign = false
if value >= 0.0:
if spec.sign != '-':
f = spec.sign & f
sign = true
if value == 0.0:
if 1.0 / value == Inf:
# only add the sign if value != negZero
f = spec.sign & f
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Could you use insert instead, to modify 'f' in place? It would be nice to reduce the number of temporary string allocations made in this procedure.

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There are other places where we could use insert instead of string concatenation, but i limit the change strictly to the area i want to fix (no + in front of negative zero).

Personally i don't like inplace mutations, therefore I will not produce PR's to change other places in strformat to use inplace mutations.

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It doesn't matter if you like them or not, they are faster and this is a "standard library" where everybody benefits from faster code.

else:
f = spec.sign & f
else:
sign = true

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8 changes: 8 additions & 0 deletions tests/stdlib/tstrformat.nim
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Expand Up @@ -20,3 +20,11 @@ doAssert fmt"{-1.5:0>8}" == "0000-1.5" # even that does not work for negative fl
doAssert fmt"{-1.5:08}" == "-00001.5" # works
doAssert fmt"{1.5:+08}" == "+00001.5" # works
doAssert fmt"{1.5: 08}" == " 00001.5" # works

# only add explicitly requested sign if value != -0.0 (neg zero)
doAssert fmt"{-0.0:g}" == "-0"
doassert fmt"{-0.0:+g}" == "-0"
doassert fmt"{-0.0: g}" == "-0"
doAssert fmt"{0.0:g}" == "0"
doAssert fmt"{0.0:+g}" == "+0"
doAssert fmt"{0.0: g}" == " 0"