72 lines
4.0 KiB
Nim
72 lines
4.0 KiB
Nim
import std/parseutils; export parseutils
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#From https://github.com/nim-lang/Nim/pull/21349 in -devel and in version-1-6:
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# https://github.com/nim-lang/Nim/commit/c546ba5d23bb2e7bc562a071c88efd94cca7b89e
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# https://github.com/nim-lang/Nim/commit/fca6a0bd6a6d3b9a25d1272e29bc39e88853188e
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when not declared(parseSize): # Odd code formatting to minimize diff v. mainLine
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const Whitespace = {' ', '\t', '\v', '\r', '\l', '\f'}
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func toLowerAscii(c: char): char =
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if c in {'A'..'Z'}: char(uint8(c) xor 0b0010_0000'u8) else: c
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func parseSize*(s: string, size: var int64, alwaysBin=false): int =
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## Parse a size qualified by binary or metric units into `size`. This format
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## is often called "human readable". Result is the number of processed chars
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## or 0 on parse errors and size is rounded to the nearest integer. Trailing
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## garbage like "/s" in "1k/s" is allowed and detected by `result < s.len`.
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##
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## To simplify use, following non-rare wild conventions, and since fractional
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## data like milli-bytes is so rare, unit matching is case-insensitive but for
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## the 'i' distinguishing binary-metric from metric (which cannot be 'I').
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##
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## An optional trailing 'B|b' is ignored but processed. I.e., you must still
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## know if units are bytes | bits or infer this fact via the case of s[^1] (if
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## users can even be relied upon to use 'B' for byte and 'b' for bit or have
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## that be s[^1]).
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##
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## If `alwaysBin==true` then scales are always binary-metric, but e.g. "KiB"
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## is still accepted for clarity. If the value would exceed the range of
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## `int64`, `size` saturates to `int64.high`. Supported metric prefix chars
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## include k, m, g, t, p, e, z, y (but z & y saturate unless the number is a
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## small fraction).
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##
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## **See also:**
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## * https://en.wikipedia.org/wiki/Binary_prefix
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## * `formatSize module<strutils.html>`_ for formatting
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runnableExamples:
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var res: int64 # caller must still know if 'b' refers to bytes|bits
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doAssert parseSize("10.5 MB", res) == 7
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doAssert res == 10_500_000 # decimal metric Mega prefix
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doAssert parseSize("64 mib", res) == 6
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doAssert res == 67108864 # 64 shl 20
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doAssert parseSize("1G/h", res, true) == 2 # '/' stops parse
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doAssert res == 1073741824 # 1 shl 30, forced binary metric
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const prefix = "b" & "kmgtpezy" # byte|bit & lowCase metric-ish prefixes
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const scaleM = [1.0, 1e3, 1e6, 1e9, 1e12, 1e15, 1e18, 1e21, 1e24] # 10^(3*idx)
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const scaleB = [1.0, 1024, 1048576, 1073741824, 1099511627776.0, # 2^(10*idx)
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1125899906842624.0, 1152921504606846976.0, # ldexp?
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1.180591620717411303424e21, 1.208925819614629174706176e24]
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var number: float
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var scale = 1.0
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result = parseFloat(s, number)
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if number < 0: # While parseFloat accepts negatives ..
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result = 0 #.. we do not since sizes cannot be < 0
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if result > 0:
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let start = result # Save spot to maybe unwind white to EOS
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while result < s.len and s[result] in Whitespace:
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inc result
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if result < s.len: # Illegal starting char => unity
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if (let si = prefix.find(s[result].toLowerAscii); si >= 0):
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inc result # Now parse the scale
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scale = if alwaysBin: scaleB[si] else: scaleM[si]
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if result < s.len and s[result] == 'i':
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scale = scaleB[si] # Switch from default to binary-metric
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inc result
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if result < s.len and s[result].toLowerAscii == 'b':
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inc result # Skip optional '[bB]'
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else: # Unwind result advancement when there..
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result = start #..is no unit to the end of `s`.
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var sizeF = number * scale + 0.5 # Saturate to int64.high when too big
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size = if sizeF > 9223372036854774784.0: int64.high else: sizeF.int64
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# Above constant=2^63-1024 avoids C UB; github.com/nim-lang/Nim/issues/20102 or
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# stackoverflow.com/questions/20923556/math-pow2-63-1-math-pow2-63-512-is-true
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