Found how to improve performance of the access operators

[planetis-m]

Currently there's a consisted 50% decrease in performance (0.22ms -> 0.44ms) for both short and long strings compared to std.string in the parseBinInt benchmark. Tested with gcc and clang. Using templates instead of procs for [], it drops down to ~26% (0.3ms).

[planetis-m]

Same issue as: nim-lang/Nim#18339

[planetis-m]

This change in myParseBin did not improve performance versus making [] a template

    template longData(s: String): untyped = s.p
    template shortData(s: String): untyped =
      cast[ptr UncheckedArray[char]](addr s.short.data[0])

    if s.isLong:
      while i < last:
        case s.longData[i]
        of '_': discard
        of '0'..'1':
          output = output shl 1 or T(ord(s.longData[i]) - ord('0'))
          foundDigit = true
        else: break
        inc(i)
    else:
      while i < last:
        case s.shortData[i]
        of '_': discard
        of '0'..'1':
          output = output shl 1 or T(ord(s.shortData[i]) - ord('0'))
          foundDigit = true
        else: break
        inc(i)

Results:

ParseBin std.string:
  Collected 10000 samples in 2.0677 s
  Average time: 0.2060 ms
  Stddev  time: 0.0116 ms
  Min     time: 0.2025 ms
  Max     time: 0.4008 ms

ParseBin String: # with above change
  Collected 10000 samples in 3.0586 s
  Average time: 0.3050 ms
  Stddev  time: 0.0013 ms
  Min     time: 0.3039 ms
  Max     time: 0.4171 ms

ParseBin String: # with template
  Collected 10000 samples in 2.8379 s
  Average time: 0.2830 ms
  Stddev  time: 0.0051 ms
  Min     time: 0.2816 ms
  Max     time: 0.4381 ms

ParseBin String: # Current
  Collected 10000 samples in 4.4027 s
  Average time: 0.4395 ms
  Stddev  time: 0.0091 ms
  Min     time: 0.4384 ms
  Max     time: 1.2552 ms