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parsing.go
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parsing.go
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package bivariate
import (
"regexp"
"strconv"
"strings"
"github.com/ReneBoedker/algobra/errors"
"github.com/ReneBoedker/algobra/finitefield/ff"
)
type monomialMatch struct {
qr *QuotientRing
sign string
coef string
vars [2]string
degs [2]string
}
func newMonomialMatch(match []string, op errors.Op, qr *QuotientRing) (*monomialMatch, error) {
if len(match) != 8 {
return nil, errors.New(
op, errors.Parsing,
"Regexp-match has unexpected form (%q)", match,
)
}
out := &monomialMatch{
qr: qr,
sign: match[1],
coef: match[2] + match[7],
vars: [2]string{
strings.ToLower(match[3]),
strings.ToLower(match[5]),
},
degs: [2]string{
match[4],
match[6],
},
}
// Check that the match is not only a sign
if out.coef == "" && out.vars == [2]string{"", ""} && out.degs == [2]string{"", ""} {
return nil, errors.New(
op, errors.Parsing,
"Found regexp-match containing only a sign (full match %q)", match[0],
)
}
err := out.ensureVariableOrder(op)
if err != nil {
return nil, err
}
return out, nil
}
func (m *monomialMatch) ensureVariableOrder(op errors.Op) error {
varLower := [2]string{
strings.ToLower(m.qr.varNames[0]),
strings.ToLower(m.qr.varNames[1]),
}
switch {
case m.vars[0] == varLower[0] && (m.vars[1] == varLower[1] || m.vars[1] == ""):
// Correct; do nothing
case m.vars[0] == varLower[1] && (m.vars[1] == varLower[0] || m.vars[1] == ""):
m.vars[0], m.vars[1] = m.vars[1], m.vars[0]
m.degs[0], m.degs[1] = m.degs[1], m.degs[0]
case m.vars[0] == "" && m.vars[1] == "":
// Correct; do nothing
default:
return errors.New(
op, errors.Parsing,
"Unexpected variable names in match %v", m,
)
}
return nil
}
func (m *monomialMatch) degreesAndCoef(op errors.Op) (deg [2]uint, coef ff.Element, err error) {
if m.coef == "" {
coef = m.qr.baseField.One()
} else {
coef, err = m.qr.baseField.ElementFromString(strings.Trim(m.coef, "()"))
if err != nil {
return deg, coef, errors.Wrap(op, errors.Conversion, err)
}
}
if m.sign == "-" {
coef.SetNeg()
}
for i := 0; i < 2; i++ {
if m.vars[i] != "" {
deg[i], err = parseExponent(m.degs[i])
if err != nil {
err = errors.Wrap(op, errors.Conversion, err)
return
}
}
}
return
}
func parseExponent(s string) (uint, error) {
if s == "" {
return 1, nil
}
tmp, err := strconv.ParseUint(s, 10, 0)
return uint(tmp), err
}
func polynomialStringToMap(s string, varNames *[2]string, qr *QuotientRing) (map[[2]uint]ff.Element, error) {
const op = "Parsing polynomial from string"
xOrY := regexp.QuoteMeta((*varNames)[0]) + `|` + regexp.QuoteMeta((*varNames)[1])
// Construct a regular expression that captures each term of a bivariate
// polynomial
pattern, err := regexp.Compile(
`(?P<sign>^|\+|-)\s*` + // A sign (or start of string)
`(?:` + // Begin group of alternatives
// First alternative: Term contains a variable
`(?P<coef>` + qr.baseField.RegexElement(true) + `)?` + // A coefficient
`\s*\*?\s*` + // Optional multiplication sign
`(?P<var1>(?i:` + xOrY + `))\^?(?P<deg1>[0-9]*)` + // Variable and optional degree
`(?:` + // Begin optional second variable
`\s*\*?\s*` + // Optional multiplication sign
`(?P<var2>(?i:` + xOrY + `))?\^?(?P<deg2>[0-9]*)` +
`)?\s*` + // End optional second variable
`|` +
// Second alternative: Term is only a coefficient
`(?P<coefOnly>` + qr.baseField.RegexElement(true) + `)\s*` +
`)`, // End group of alternatives
)
if err != nil {
return nil, errors.New(
op, errors.Internal,
"Failed to compile regular expression using variable names %q and %q",
varNames[0], varNames[1],
)
}
matches := pattern.FindAllStringSubmatch(s, -1)
// Check that total match length is the full input string
matchLen := 0
for _, m := range matches {
matchLen += len(m[0])
}
if matchLen != len(s) {
return nil, errors.New(
op, errors.Parsing,
"Cannot parse %s; lengths do not match (%d ≠ %d) %v",
s, matchLen, len(s), matches,
)
}
out := make(map[[2]uint]ff.Element)
for _, m := range matches {
tmp, err := newMonomialMatch(m, op, qr)
if err != nil {
return nil, err
}
deg, coef, err2 := tmp.degreesAndCoef(op)
if err2 != nil {
return nil, err2
}
if _, ok := out[deg]; !ok {
out[deg] = coef
} else {
out[deg].Add(coef)
}
}
return out, nil
}
/* Copyright 2019 René Bødker Christensen
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/