formatfloat.nim

#
#
# Nim's Runtime Library
# (c) Copyright 2022 Nim contributors
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#

## This module implements formatting floats as strings.

whendefined(nimPreviewSlimSystem):
import std/assertions

from system/ansi_c import c_memcpy

procaddCstringN(result: varstring, buf: cstring; buflen: int) =
# no nimvm support needed, so it doesn't need to be fast here either
let oldLen =result.len
let newLen = oldLen + buflen
result.setLen newLen
c_memcpy(result[oldLen].addr, buf, buflen.csize_t)

import std/private/[dragonbox, schubfach]

procwriteFloatToBufferRoundtrip*(buf: vararray[65, char]; value: BiggestFloat): int=
## This is the implementation to format floats.
##
## returns the amount of bytes written to `buf` not counting the
## terminating '\0' character.
result=toChars(buf, value, forceTrailingDotZero=true).int
 buf[result] ='\0'

procwriteFloatToBufferRoundtrip*(buf: vararray[65, char]; value: float32): int=
result=float32ToChars(buf, value, forceTrailingDotZero=true).int
 buf[result] ='\0'

procc_snprintf(buf: cstring, n: csize_t, frmt: cstring): cint {.header: "<stdio.h>",
importc: "snprintf", varargs, noSideEffect.}

procwriteToBuffer(buf: vararray[65, char]; value: cstring) =
var i =0
while value[i] !='\0':
 buf[i] = value[i]
inc i

procwriteFloatToBufferSprintf*(buf: vararray[65, char]; value: BiggestFloat): int=
## This is the implementation to format floats.
##
## returns the amount of bytes written to `buf` not counting the
## terminating '\0' character.
var n =c_snprintf(cast[cstring](addr buf), 65, "%.16g", value).int
var hasDot =false
for i in0..n-1:
if buf[i] ==',':
 buf[i] ='.'
 hasDot =true
elif buf[i] in {'a'..'z', 'A'..'Z', '.'}:
 hasDot =true
ifnot hasDot:
 buf[n] ='.'
 buf[n+1] ='0'
 buf[n+2] ='\0'
result= n +2
else:
result= n
# On Windows nice numbers like '1.#INF', '-1.#INF' or '1.#NAN' or 'nan(ind)'
# of '-1.#IND' are produced.
# We want to get rid of these here:
if buf[n-1] in {'n', 'N', 'D', 'd', ')'}:
writeToBuffer(buf, "nan")
result=3
elif buf[n-1] =='F':
if buf[0] =='-':
writeToBuffer(buf, "-inf")
result=4
else:
writeToBuffer(buf, "inf")
result=3

procwriteFloatToBuffer*(buf: vararray[65, char]; value: BiggestFloat|float32): int {.inline.} =
whendefined(nimLegacySprintf):
writeFloatToBufferSprintf(buf, value)
else:
writeFloatToBufferRoundtrip(buf, value)

procaddFloatRoundtrip*(result: varstring; x: float|float32) =
whennimvm:
raiseAssert"unreachable"
else:
var buffer {.noinit.}: array[65, char]
let n =writeFloatToBufferRoundtrip(buffer, x)
result.addCstringN(cast[cstring](buffer[0].addr), n)

procaddFloatSprintf*(result: varstring; x: float) =
whennimvm:
raiseAssert"unreachable"
else:
var buffer {.noinit.}: array[65, char]
let n =writeFloatToBufferSprintf(buffer, x)
result.addCstringN(cast[cstring](buffer[0].addr), n)

whendefined(js):
procnimFloatToString(a: float): cstring=
## ensures the result doesn't print like an integer, i.e. return 2.0, not 2
# print `-0.0` properly
 {.emit: """
 function nimOnlyDigitsOrMinus(n) {
 return n.toString().match(/^-?\d+$/);
 }
 if (Number.isSafeInteger(`a`))
 `result` = `a` === 0 && 1 / `a` < 0 ? "-0.0" : `a`+".0";
 else if (isNaN(`a`)) // Number.isNaN is since ES6
 `result` = "nan"; // or it'll be "NaN"
 else if (!isFinite(`a`)) // Number.isFinite newer but unnecessary here
 `result` = `a` > 0 ? "inf" : "-inf"; // or it'll be [-]Infinity
 else {
 `result` = `a`+"";
 if(nimOnlyDigitsOrMinus(`result`)){
 `result` = `a`+".0";
 }
 }
""".}

procaddFloat*(result: varstring; x: float|float32) {.inline.} =
## Converts float to its string representation and appends it to `result`.
 runnableExamples:
var
 s ="foo:"
 b =45.67
 s.addFloat(45.67)
assert s =="foo:45.67"
templateimpl=
whendefined(nimLegacySprintf):
addFloatSprintf(result, x)
else:
addFloatRoundtrip(result, x)
whendefined(js):
whennimvm: impl()
else:
result.addnimFloatToString(x)
else: impl()

whendefined(nimPreviewSlimSystem):
func`$`*(x: float|float32): string=
## Outplace version of `addFloat`.
result.addFloat(x)