writeText for float rewritten to re-use Nim's call to sprintf

faststreams/textio.nim

@@ -1,7 +1,7 @@
 import
   stew/ptrops,
   inputs, outputs, buffers, async_backend, multisync,
-  math
+  system/formatfloat
 
 template matchingIntType(T: type int64): type = uint64
 template matchingIntType(T: type int32): type = uint32
@@ -92,149 +92,22 @@ proc writeText*(s: OutputStream, x: CompiledIntTypes) =
   else:
     writeText(s, MatchingUInt(x))
 
-when defined(aa):
-  proc writeText*(s: OutputStream, x: float64|float) =  # this version mostly works, but does not account for rounding error
-    var whole = x.int
-    writeText(s, whole)
-    var frac = abs(x - whole.float)
-    if frac == 0.0:
-      return
-    write s, '.'
-    var limit: byte = 8
-    while (frac != 0.0) and (limit > 0):
-      limit -= 1
-      frac *=  10.0
-      whole = frac.int
-      frac -= whole.float
-      write s, char(ord('0') + whole)
-
-when defined(bb):
-  proc writeText*(s: OutputStream, x: float64|float) =   # this version just prints the integer part
-    writeText(s, x.int)
-
-when defined(cc):
-  proc writeText*(s: OutputStream, x: float64|float) =   # this version uses ftoa of stdlibc
-    proc floatToStr(x: float): string {.magic: "FloatToStr", noSideEffect.}
-    writeText(s, floatToStr(x))
-
-when defined(dd):
-  proc writeText*(s: OutputStream, x: float64|float) =   # this version uses ftoa of stdlibc
-    write s, $x
-
-when defined(ee):
-  proc writeText*(s: OutputStream, x: float64|float) =  # this version mostly works, but does not account for rounding error
-    if x == 0.0:
-      write s, "0.0"
-      return
-    if x < 0.0:
-      write s, '-'
-    var frac = x.abs
-    var place = log10(frac).int
-    if place < 0:
-      place = 0
-    frac /= pow(10.0, place.float)
-    var whole: int
-    while (frac != 0.0) and (place > -100):
-      if place == -1:
-        write s, '.'
-      whole = frac.int
-      write s, char(ord('0') + whole)
-      frac = (frac - whole.float) * 10.0
-      place -= 1
-
-when defined(ff):
-  proc writeText*(s: OutputStream, x: float64|float) =  # handles rounding
-    const PRECISION_LIMIT = 16
-    const DECIMAL_POINT: uint8 = 255
-    if x == 0.0:
-      write s, "0.0"
-      return
-    var digits: array[322, byte]
-    var index: int = 0
-    if x < 0.0:
-      write s, '-'
-    var precision: int = 0
-    var firstDigitFound = false
-    var decimalPointIndex = -1
-    var frac = x.abs
-    var place = log10(frac).int
-    if place < 0:
-      place = 0
-    frac /= pow(10.0, place.float)
-    var whole: uint8
-    #
-    # run through the digits:
-    #
-    while (frac != 0.0) and (place > -317) and (precision < PRECISION_LIMIT):
-      if place == -1:
-        digits[index] = DECIMAL_POINT
-        decimalPointIndex = index
-        index += 1
-      whole = frac.uint8
-      digits[index] = whole
-      index += 1
-      if firstDigitFound:
-        precision += 1
-      else:
-        if whole != 0.uint8:
-          firstDigitFound = true
-          precision += 1
-      frac = (frac - whole.float) * 10.0
-      place -= 1
-    #
-    # place any missing decimal points as a key marker
-    #
-    if decimalPointIndex == -1:
-      # if decimal point not expressed yet, then add it
-      index += place + 1
-      digits[index] = DECIMAL_POINT
-      decimalPointIndex = index
-      index += 1
-    index -= 1
-    #
-    # remove trailing digits and adjust precision back if need be:
-    #
-    while (digits[index] == 0) and (index > 0):
-      precision -= 1
-      index -= 1
-    #
-    # if still at precision limit, then do rounding:
-    #
-    if precision >= PRECISION_LIMIT:
-      while index > 0:
-        if digits[index] == DECIMAL_POINT:
-          index -= 1
-          continue
-        elif digits[index] >= 5:
-          digits[index - 1] += 1
-          digits[index] = 0
-          if digits[index - 1] < 10:
-            break
-        else:
-          digits[index] = 0
-          break
-        index -= 1
-    #
-    # remove trailing digits and adjust precision back if need be:
-    #
-    while (digits[index] == 0) and (index > 0):
-      precision -= 1
-      index -= 1
-    #
-    # express to the stream
-    #
-    if index < decimalPointIndex:
-      index = decimalPointIndex
-    for i in 0 .. index:
-      let d = digits[i]
-      if d == DECIMAL_POINT:
-        write s, '.'
-      elif d == 10:
-        write s, "10"
-      else:
-        write s, char(ord('0') + d)
-    if digits[index] == DECIMAL_POINT:
-      write s, '0'
+when defined(c):
+  
+  proc writeText*(s: OutputStream, x: float64|float32|float) =
+    ## Write the floating point number to the output stream. It has less overhead
+    ## than `$` because it is directly written to the stream without
+    ## allocating a standard Nim 'string'.
+    ##
+    ## Because this procedure uses stdlib, it is only active when nim compiles
+    ## with the 'c' flag. Otherwise, float types fall back to the generic writeText
+    ## procedure.
+    var buffer: array[65, char]
+    discard writeFloatToBuffer(buffer, x)
+    for index in 0 ..< 65:
+      if buffer[index] == '\0':
+        break
+      write s, buffer[index]
 
 template writeText*(s: OutputStream, str: string) =
   write s, str