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236 lines
7 KiB
Go
236 lines
7 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package colltab
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import (
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"unicode"
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"unicode/utf8"
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)
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// NewNumericWeighter wraps w to replace individual digits to sort based on their
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// numeric value.
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//
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// Weighter w must have a free primary weight after the primary weight for 9.
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// If this is not the case, numeric value will sort at the same primary level
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// as the first primary sorting after 9.
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func NewNumericWeighter(w Weighter) Weighter {
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getElem := func(s string) Elem {
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elems, _ := w.AppendNextString(nil, s)
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return elems[0]
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}
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nine := getElem("9")
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// Numbers should order before zero, but the DUCET has no room for this.
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// TODO: move before zero once we use fractional collation elements.
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ns, _ := MakeElem(nine.Primary()+1, nine.Secondary(), int(nine.Tertiary()), 0)
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return &numericWeighter{
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Weighter: w,
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// We assume that w sorts digits of different kinds in order of numeric
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// value and that the tertiary weight order is preserved.
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//
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// TODO: evaluate whether it is worth basing the ranges on the Elem
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// encoding itself once the move to fractional weights is complete.
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zero: getElem("0"),
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zeroSpecialLo: getElem("０"), // U+FF10 FULLWIDTH DIGIT ZERO
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zeroSpecialHi: getElem("₀"), // U+2080 SUBSCRIPT ZERO
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nine: nine,
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nineSpecialHi: getElem("₉"), // U+2089 SUBSCRIPT NINE
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numberStart: ns,
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}
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}
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// A numericWeighter translates a stream of digits into a stream of weights
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// representing the numeric value.
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type numericWeighter struct {
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Weighter
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// The Elems below all demarcate boundaries of specific ranges. With the
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// current element encoding digits are in two ranges: normal (default
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// tertiary value) and special. For most languages, digits have collation
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// elements in the normal range.
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//
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// Note: the range tests are very specific for the element encoding used by
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// this implementation. The tests in collate_test.go are designed to fail
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// if this code is not updated when an encoding has changed.
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zero Elem // normal digit zero
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zeroSpecialLo Elem // special digit zero, low tertiary value
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zeroSpecialHi Elem // special digit zero, high tertiary value
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nine Elem // normal digit nine
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nineSpecialHi Elem // special digit nine
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numberStart Elem
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}
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// AppendNext calls the namesake of the underlying weigher, but replaces single
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// digits with weights representing their value.
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func (nw *numericWeighter) AppendNext(buf []Elem, s []byte) (ce []Elem, n int) {
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ce, n = nw.Weighter.AppendNext(buf, s)
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nc := numberConverter{
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elems: buf,
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w: nw,
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b: s,
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}
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isZero, ok := nc.checkNextDigit(ce)
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if !ok {
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return ce, n
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}
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// ce might have been grown already, so take it instead of buf.
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nc.init(ce, len(buf), isZero)
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for n < len(s) {
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ce, sz := nw.Weighter.AppendNext(nc.elems, s[n:])
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nc.b = s
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n += sz
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if !nc.update(ce) {
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break
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}
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}
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return nc.result(), n
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}
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// AppendNextString calls the namesake of the underlying weigher, but replaces
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// single digits with weights representing their value.
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func (nw *numericWeighter) AppendNextString(buf []Elem, s string) (ce []Elem, n int) {
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ce, n = nw.Weighter.AppendNextString(buf, s)
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nc := numberConverter{
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elems: buf,
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w: nw,
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s: s,
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}
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isZero, ok := nc.checkNextDigit(ce)
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if !ok {
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return ce, n
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}
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nc.init(ce, len(buf), isZero)
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for n < len(s) {
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ce, sz := nw.Weighter.AppendNextString(nc.elems, s[n:])
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nc.s = s
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n += sz
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if !nc.update(ce) {
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break
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}
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}
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return nc.result(), n
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}
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type numberConverter struct {
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w *numericWeighter
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elems []Elem
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nDigits int
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lenIndex int
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s string // set if the input was of type string
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b []byte // set if the input was of type []byte
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}
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// init completes initialization of a numberConverter and prepares it for adding
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// more digits. elems is assumed to have a digit starting at oldLen.
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func (nc *numberConverter) init(elems []Elem, oldLen int, isZero bool) {
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// Insert a marker indicating the start of a number and and a placeholder
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// for the number of digits.
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if isZero {
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elems = append(elems[:oldLen], nc.w.numberStart, 0)
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} else {
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elems = append(elems, 0, 0)
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copy(elems[oldLen+2:], elems[oldLen:])
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elems[oldLen] = nc.w.numberStart
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elems[oldLen+1] = 0
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nc.nDigits = 1
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}
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nc.elems = elems
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nc.lenIndex = oldLen + 1
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}
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// checkNextDigit reports whether bufNew adds a single digit relative to the old
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// buffer. If it does, it also reports whether this digit is zero.
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func (nc *numberConverter) checkNextDigit(bufNew []Elem) (isZero, ok bool) {
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if len(nc.elems) >= len(bufNew) {
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return false, false
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}
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e := bufNew[len(nc.elems)]
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if e < nc.w.zeroSpecialLo || nc.w.nine < e {
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// Not a number.
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return false, false
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}
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if e < nc.w.zero {
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if e > nc.w.nineSpecialHi {
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// Not a number.
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return false, false
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}
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if !nc.isDigit() {
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return false, false
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}
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isZero = e <= nc.w.zeroSpecialHi
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} else {
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// This is the common case if we encounter a digit.
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isZero = e == nc.w.zero
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}
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// Test the remaining added collation elements have a zero primary value.
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if n := len(bufNew) - len(nc.elems); n > 1 {
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for i := len(nc.elems) + 1; i < len(bufNew); i++ {
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if bufNew[i].Primary() != 0 {
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return false, false
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}
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}
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// In some rare cases, collation elements will encode runes in
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// unicode.No as a digit. For example Ethiopic digits (U+1369 - U+1371)
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// are not in Nd. Also some digits that clearly belong in unicode.No,
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// like U+0C78 TELUGU FRACTION DIGIT ZERO FOR ODD POWERS OF FOUR, have
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// collation elements indistinguishable from normal digits.
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// Unfortunately, this means we need to make this check for nearly all
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// non-Latin digits.
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//
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// TODO: check the performance impact and find something better if it is
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// an issue.
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if !nc.isDigit() {
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return false, false
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}
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}
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return isZero, true
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}
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func (nc *numberConverter) isDigit() bool {
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if nc.b != nil {
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r, _ := utf8.DecodeRune(nc.b)
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return unicode.In(r, unicode.Nd)
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}
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r, _ := utf8.DecodeRuneInString(nc.s)
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return unicode.In(r, unicode.Nd)
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}
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// We currently support a maximum of about 2M digits (the number of primary
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// values). Such numbers will compare correctly against small numbers, but their
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// comparison against other large numbers is undefined.
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//
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// TODO: define a proper fallback, such as comparing large numbers textually or
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// actually allowing numbers of unlimited length.
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//
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// TODO: cap this to a lower number (like 100) and maybe allow a larger number
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// in an option?
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const maxDigits = 1<<maxPrimaryBits - 1
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func (nc *numberConverter) update(elems []Elem) bool {
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isZero, ok := nc.checkNextDigit(elems)
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if nc.nDigits == 0 && isZero {
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return true
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}
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nc.elems = elems
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if !ok {
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return false
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}
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nc.nDigits++
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return nc.nDigits < maxDigits
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}
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// result fills in the length element for the digit sequence and returns the
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// completed collation elements.
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func (nc *numberConverter) result() []Elem {
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e, _ := MakeElem(nc.nDigits, defaultSecondary, defaultTertiary, 0)
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nc.elems[nc.lenIndex] = e
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return nc.elems
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}
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