strm.go

// Copyright (c) 2009 Helmar Wodtke. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
// The MIT License is an OSI approved license and can
// be found at
//   http://www.opensource.org/licenses/mit-license.php

// string math
package strm

import (
  "bignum"
)

func operand(s string) (r int64, f int) {
  if len(s) < 1 {
    return 0, 1
  }
  sig := s[0] == '-'
  p := 0
  if sig {
    p++
  }
  for p < len(s) {
    if s[p] == '.' {
      f = 1
    } else {
      f *= 10
      r *= 10
      r += int64(s[p] - '0')
    }
    p++
  }
  if sig {
    r = -r
  }
  if f == 0 {
    f = 1
  }
  return
}

func Int64(s string, f int) int64 {
  ra, fa := operand(s)
  for fa < f {
    fa *= 10
    ra *= 10
  }
  return ra / int64(fa/f)
}

func Int(s string, f int) int { return int(Int64(s, f)) }

func twop(a, b string) (ra, rb int64, f int) {
  ra, f = operand(a)
  rb, fb := operand(b)
  for fb < f {
    fb *= 10
    rb *= 10
  }
  for f < fb {
    f *= 10
    ra *= 10
  }
  return
}

func String(a int64, f int) string {
  buf := make([]byte, 128)
  p := 0
  if a < 0 {
    buf[p] = '-'
    p++
    a = -a
  }
  var fu func(c int64)
  step := 1
  fu = func(c int64) {
    s := step
    step *= 10
    if c > 9 || step <= f {
      fu(c / 10)
    }
    buf[p] = '0' + byte(c%10)
    p++
    if f == s && f != 1 {
      buf[p] = '.'
      p++
    }
  }
  fu(a)
  return string(buf[0:p])
}

func Mul(a, b string) string {
  ra, rb, f := twop(a, b)
  ar := bignum.Rat(ra, int64(f))
  br := bignum.Rat(rb, int64(f))
  i, n := ar.Mul(br).Value()
  nv := n.Value()
  d := uint64(1)
  for d%nv != 0 {
    d *= 10
  }
  i = i.Mul1(int64(d / nv))
  if uint64(f) < d {
    i = i.Div(bignum.Int(int64(d / uint64(f))))
    d = uint64(f)
  }
  return String(i.Value(), int(d))
}

func Add(a, b string) string {
  ra, rb, f := twop(a, b)
  return String(ra+rb, f)
}

func Sub(a, b string) string {
  ra, rb, f := twop(a, b)
  return String(ra-rb, f)
}

func Neg(a string) string {
  if a[0] == '-' {
    return a[1:len(a)]
  }
  ra, f := operand(a)
  return String(-ra, f)
}

func Percent(c []byte) []byte { // convert 0..1 color lossless to percent
  r := make([]byte, len(c)+2)
  p := 0
  d := -111
  q := 0
  for p < len(c) {
    if d == p-3 {
      r[q] = '.'
      q++
    }
    if c[p] == '.' {
      d = p
    } else {
      r[q] = c[p]
      q++
    }
    p++
  }
  if d == -111 || d == p-1 {
    r[q] = '0'
    q++
    r[q] = '0'
    q++
  }
  if d == p-2 {
    r[q] = '0'
    q++
  }
  for p = 0; p < q-1 && r[p] == '0'; p++ {
  }
  return r[p:q]
}