newStringOfCap implemented and used to optimize some procs

lib/pure/cgi.nim

@@ -36,7 +36,7 @@ proc URLencode*(s: string): string =
   ## ``{'A'..'Z', 'a'..'z', '0'..'9', '_'}`` are carried over to the result,
   ## a space is converted to ``'+'`` and every other character is encoded as
   ## ``'%xx'`` where ``xx`` denotes its hexadecimal value. 
-  result = ""
+  result = newStringOfCap(s.len + s.len shr 2) # assume 12% non-alnum-chars
   for i in 0..s.len-1:
     case s[i]
     of 'a'..'z', 'A'..'Z', '0'..'9', '_': add(result, s[i])
@@ -57,8 +57,9 @@ proc URLdecode*(s: string): string =
   ## is converted to a space, ``'%xx'`` (where ``xx`` denotes a hexadecimal
   ## value) is converted to the character with ordinal number ``xx``, and  
   ## and every other character is carried over. 
-  result = ""
+  result = newString(s.len)
   var i = 0
+  var j = 0
   while i < s.len:
     case s[i]
     of '%': 
@@ -66,10 +67,12 @@ proc URLdecode*(s: string): string =
       handleHexChar(s[i+1], x)
       handleHexChar(s[i+2], x)
       inc(i, 2)
-      add(result, chr(x))
-    of '+': add(result, ' ')
-    else: add(result, s[i])
+      result[j] = chr(x)
+    of '+': result[j] = ' '
+    else: result[j] = s[i]
     inc(i)
+    inc(j)
+  setLen(result, j)
 
 proc addXmlChar(dest: var string, c: Char) {.inline.} = 
   case c
@@ -86,7 +89,7 @@ proc XMLencode*(s: string): string =
   ## * ``>`` is replaced by ``&gt;``
   ## * ``&`` is replaced by ``&amp;``
   ## * every other character is carried over.
-  result = ""
+  result = newStringOfCap(s.len + s.len shr 2)
   for i in 0..len(s)-1: addXmlChar(result, s[i])
 
 type
@@ -367,4 +370,8 @@ proc existsCookie*(name: string): bool =
   if gcookies == nil: gcookies = parseCookies(getHttpCookie())
   result = hasKey(gcookies, name)
 
+when isMainModule:
+  const test1 = "abc\L+def xyz"
+  assert UrlEncode(test1) == "abc%0A%2Bdef+xyz"
+  assert UrlDecode(UrlEncode(test1)) == test1
 

lib/pure/json.nim

@@ -620,7 +620,8 @@ proc nl(s: var string, ml: bool) =
 
 proc escapeJson*(s: string): string = 
   ## Converts a string `s` to its JSON representation.
-  result = "\""
+  result = newStringOfCap(s.len + s.len shr 3)
+  result.add("\"")
   for x in runes(s):
     var r = int(x)
     if r >= 32 and r <= 127:

lib/pure/strutils.nim

@@ -89,12 +89,16 @@ proc normalize*(s: string): string {.noSideEffect, procvar,
   rtl, extern: "nsuNormalize".} =
   ## Normalizes the string `s`. That means to convert it to lower case and
   ## remove any '_'. This is needed for Nimrod identifiers for example.
-  result = ""
+  result = newString(s.len)
+  var j = 0
   for i in 0..len(s) - 1:
     if s[i] in {'A'..'Z'}:
-      add result, Chr(Ord(s[i]) + (Ord('a') - Ord('A')))
+      result[j] = Chr(Ord(s[i]) + (Ord('a') - Ord('A')))
+      inc j
     elif s[i] != '_':
-      add result, s[i]
+      result[j] = s[i]
+      inc j
+  if j != s.len: setLen(result, j)
 
 proc cmpIgnoreCase*(a, b: string): int {.noSideEffect,
   rtl, extern: "nsuCmpIgnoreCase", procvar.} =
@@ -226,13 +230,14 @@ proc `%` *(formatstr: string, a: openarray[string]): string {.noSideEffect,
   ##
   ## The variables are compared with `cmpIgnoreStyle`. `EInvalidValue` is
   ## raised if an ill-formed format string has been passed to the `%` operator.
-  result = ""
+  result = newStringOfCap(formatstr.len + a.len shl 4)
   addf(result, formatstr, a)
 
 proc `%` *(formatstr, a: string): string {.noSideEffect, 
   rtl, extern: "nsuFormatSingleElem".} =
   ## This is the same as ``formatstr % [a]``.
-  return formatstr % [a]
+  result = newStringOfCap(formatstr.len + a.len)
+  addf(result, formatstr, [a])
 
 proc strip*(s: string, leading = true, trailing = true): string {.noSideEffect,
   rtl, extern: "nsuStrip".} =
@@ -510,7 +515,7 @@ proc wordWrap*(s: string, maxLineWidth = 80,
                newLine = "\n"): string {.
                noSideEffect, rtl, extern: "nsuWordWrap".} = 
   ## word wraps `s`.
-  result = ""
+  result = newStringOfCap(s.len + s.len shr 6)
   var SpaceLeft = maxLineWidth
   for word, isSep in tokenize(s, seps):
     if len(word) > SpaceLeft:
@@ -804,7 +809,8 @@ proc escape*(s: string, prefix = "\"", suffix = "\""): string {.noSideEffect,
   ## The procedure has been designed so that its output is usable for many
   ## different common syntaxes. The resulting string is prefixed with
   ## `prefix` and suffixed with `suffix`. Both may be empty strings.
-  result = prefix
+  result = newStringOfCap(s.len + s.len shr 2)
+  result.add(prefix)
   for c in items(s):
     case c
     of '\0'..'\31', '\128'..'\255':

lib/system.nim

@@ -685,7 +685,13 @@ proc newString*(len: int): string {.
   ## content. One needs to fill the string character after character
   ## with the index operator ``s[i]``. This procedure exists only for
   ## optimization purposes; the same effect can be achieved with the
-  ## ``&`` operator.
+  ## ``&`` operator or with ``add``.
+
+proc newStringOfCap*(cap: int): string {.
+  magic: "NewStringOfCap", importc: "rawNewString", noSideEffect.}
+  ## returns a new string of length ``0`` but with capacity `cap`.This
+  ## procedure exists only for optimization purposes; the same effect can 
+  ## be achieved with the ``&`` operator or with ``add``.
 
 proc `&` * (x: string, y: char): string {.
   magic: "ConStrStr", noSideEffect, merge.}