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simplify.jai
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simplify.jai
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#scope_module
compute_simple :: (using re: *Regexp_Node) -> bool {
if #complete op == {
case .NoMatch; #through;
case .EmptyMatch; #through;
case .Literal; #through;
case .LiteralString; #through;
case .BeginLine; #through;
case .EndLine; #through;
case .BeginText; #through;
case .WordBoundary; #through;
case .NoWordBoundary; #through;
case .EndText; #through;
case .AnyChar; #through;
case .AnyByte; #through;
case .HaveMatch;
return true;
case .Concat; #through;
case .Alternate;
// These are simple as long as the subpieces are simple.
for subs {
if !it.simple return false;
}
return true;
case .CharClass;
// Simple as long as the char class is not empty, not full.
return char_class.nrunes != 0 && char_class.nrunes != Runemax + 1;
case .Capture;
return subs[0].simple;
case .Star; #through;
case .Plus; #through;
case .Quest;
if !subs[0].simple return false;
if subs[0].op == {
case .Star; #through;
case .Plus; #through;
case .Quest; #through;
case .EmptyMatch; #through;
case .NoMatch;
return false;
case;
return true;
}
case .Repeat;
return false;
case .kVerticalBar; #through;
case .kLeftParen;
assert(false, "Found parser tokens in compute_simple: %", op);
return false;
}
}
// Simplifies a regular expression, returning a new regexp.
// The new regexp uses traditional Unix egrep features only,
// plus the Perl (?:) non-capturing parentheses.
// Otherwise, no POSIX or Perl additions. The new regexp
// captures exactly the same subexpressions (with the same indices)
// as the original.
// Does not edit given Regexp_Node.
simplify :: (re: *Regexp_Node, pool: *Regexp_Pool) -> *Regexp_Node {
cre := coalesce(re, pool);
if !cre return null;
sre := simplify_coalesced(cre, pool);
if !sre return null;
return sre;
}
// Coalesces runs of star/plus/quest/repeat of the same literal along with any
// occurrences of that literal into repeats of that literal. It also works for
// char classes, any char and any byte.
coalesce :: (using re: *Regexp_Node, pool: *Regexp_Pool) -> *Regexp_Node {
coalesce_post :: (pool: *Regexp_Pool, re: *Regexp_Node, parent_arg: *Regexp_Node, pre_arg: *Regexp_Node, child_args: [..] *Regexp_Node) -> *Regexp_Node {
if re.subs.count == 0 return re;
if re.op != .Concat {
if !child_args_changed(re, child_args) return re;
// Something changed. Build a new op.
nre := new_regexp(pool, re.op, re.parse_flags);
// @ToDo: Should we copy here?
nre.subs = child_args;
// Repeats and Captures have additional data that must be copied.
if (re.op == .Repeat) {
nre.min = re.min;
nre.max = re.max;
} else if re.op == .Capture {
nre.cap = re.cap;
}
return nre;
}
can_coalesce_any := false;
for i: 0..child_args.count - 2 {
if can_coalesce(child_args[i], child_args[i+1]) {
can_coalesce_any = true;
break;
}
}
if !can_coalesce_any {
if !child_args_changed(re, child_args) return re;
// Something changed. Build a new op.
nre := new_regexp(pool, re.op, re.parse_flags);
// @ToDo: Should we copy here?
nre.subs = child_args;
return nre;
}
// @Speed: Do this in one pass with the loop above?
for i: 0..child_args.count - 2 {
if can_coalesce(child_args[i], child_args[i+1]) {
do_coalesce(pool, *child_args[i], *child_args[i+1]);
}
}
// Determine how many empty matches were left by DoCoalesce.
n := 0;
for child_args {
if (it.op == .EmptyMatch) {
n += 1;
}
}
// Build a new op.
nre := new_regexp(pool, re.op, re.parse_flags);
nre.subs = NewArray(re.subs.count - n, *Regexp_Node, false);
j := 0;
for child_args {
if (it.op != .EmptyMatch) {
nre.subs[j] = it;
j += 1;
}
}
return nre;
}
w := Walk(*Regexp_Pool, *Regexp_Node).{post_visit = coalesce_post};
result, stopped := walk(pool, re, null, w);
if stopped return null;
return result;
}
child_args_changed :: (re: *Regexp_Node, child_args: [] *Regexp_Node) -> bool {
for sub, i: re.subs {
if sub != child_args[i] return true;
}
return false;
}
can_coalesce :: (r1: *Regexp_Node, r2: *Regexp_Node) -> bool {
// r1 must be a star/plus/quest/repeat of a literal, char class, any char or
// any byte.
if ((r1.op == .Star ||
r1.op == .Plus ||
r1.op == .Quest ||
r1.op == .Repeat) &&
(r1.subs[0].op == .Literal ||
r1.subs[0].op == .CharClass ||
r1.subs[0].op == .AnyChar ||
r1.subs[0].op == .AnyByte)) {
// r2 must be a star/plus/quest/repeat of the same literal, char class,
// any char or any byte.
if ((r2.op == .Star ||
r2.op == .Plus ||
r2.op == .Quest ||
r2.op == .Repeat) &&
regexp_equal(r1.subs[0], r2.subs[0]) &&
// The parse flags must be consistent.
((r1.parse_flags & .NonGreedy) == (r2.parse_flags & .NonGreedy))) {
return true;
}
// ... OR an occurrence of that literal, char class, any char or any byte
if (regexp_equal(r1.subs[0], r2)) {
return true;
}
// ... OR a literal string that begins with that literal.
if (r1.subs[0].op == .Literal && r2.op == .LiteralString && r2.runes[0] == r1.subs[0].rune &&
// The parse flags must be consistent.
((r1.subs[0].parse_flags & .FoldCase) == (r2.parse_flags & .FoldCase))) {
return true;
}
}
return false;
}
do_coalesce :: (pool: *Regexp_Pool, r1ptr: **Regexp_Node, r2ptr: **Regexp_Node) {
leave_empty :: (r1ptr: **Regexp_Node, r2ptr: **Regexp_Node, pool: *Regexp_Pool, nre: *Regexp_Node) {
// @ToDo, @Speed: Why don’t we set this to null instead of allocing a temporary new regexp?
<<r1ptr = new_regexp(pool, .EmptyMatch, .NoParseFlags);
<<r2ptr = nre;
}
r1 := <<r1ptr;
r2 := <<r2ptr;
nre := new_repeat(pool, r1.subs[0], r1.parse_flags, 0, 0);
if r1.op == {
case .Star;
nre.min = 0;
nre.max = -1;
case .Plus;
nre.min = 1;
nre.max = -1;
case .Quest;
nre.min = 0;
nre.max = 1;
case .Repeat;
nre.min = r1.min;
nre.max = r1.max;
case;
assert(false, "Unexpected r1.op: %", r1.op);
}
if r2.op == {
case .Star;
nre.max = -1;
leave_empty(r1ptr, r2ptr, pool, nre);
case .Plus;
nre.min += 1;
nre.max = -1;
leave_empty(r1ptr, r2ptr, pool, nre);
case .Quest;
if nre.max != -1 {
nre.max += 1;
}
leave_empty(r1ptr, r2ptr, pool, nre);
case .Repeat;
nre.min += r2.min;
if (r2.max == -1) {
nre.max = -1;
} else if (nre.max != -1) {
nre.max += r2.max;
}
leave_empty(r1ptr, r2ptr, pool, nre);
case .Literal; #through;
case .CharClass; #through;
case .AnyChar; #through;
case .AnyByte;
nre.min += 1;
if (nre.max != -1) {
nre.max += 1;
}
leave_empty(r1ptr, r2ptr, pool, nre);
case .LiteralString;
r := r1.subs[0].rune;
// Determine how much of the literal string is removed.
// We know that we have at least one rune. :)
n: s16 = 1;
while (n < r2.runes.count && r2.runes[n] == r) {
n += 1;
}
nre.min += n;
if (nre.max != -1) {
nre.max += n;
}
if n == r2.runes.count {
leave_empty(r1ptr, r2ptr, pool, nre);
} else {
<<r1ptr = nre;
<<r2ptr = new_literal_string(pool, slice(r2.runes, n, r2.runes.count - n), r2.parse_flags);
}
case;
assert(false, "Unexpected r2.op: %", r2.op);
}
}
simplify_coalesced :: (using re: *Regexp_Node, pool: *Regexp_Pool) -> *Regexp_Node {
simplify_pre :: (pool: *Regexp_Pool, re: *Regexp_Node, parent_arg: *Regexp_Node) -> *Regexp_Node, stop: bool {
if (re.simple) {
return re, true;
}
return null, false;
}
simplify_post :: (pool: *Regexp_Pool, re: *Regexp_Node, parent_arg: *Regexp_Node, pre_arg: *Regexp_Node, child_args: [..] *Regexp_Node) -> *Regexp_Node {
if re.op == {
case .NoMatch; #through;
case .EmptyMatch; #through;
case .Literal; #through;
case .LiteralString; #through;
case .BeginLine; #through;
case .EndLine; #through;
case .BeginText; #through;
case .WordBoundary; #through;
case .NoWordBoundary; #through;
case .EndText; #through;
case .AnyChar; #through;
case .AnyByte; #through;
case .HaveMatch;
// All these are always simple.
re.simple = true;
return re;
case .Concat; #through;
case .Alternate;
// These are simple as long as the subpieces are simple.
if !child_args_changed(re, child_args) {
re.simple = true;
return re;
}
nre := new_regexp(pool, re.op, re.parse_flags);
// @ToDo: Should we copy here?
nre.subs = child_args;
nre.simple = true;
return nre;
case .Capture;
newsub := child_args[0];
if newsub == re.subs[0] {
re.simple = true;
return re;
}
nre := new_regexp(pool, .Capture, re.parse_flags);
nre.subs = NewArray(1, *Regexp_Node, false);
nre.subs[0] = newsub;
nre.cap = re.cap;
nre.simple = true;
return nre;
case .Star; #through;
case .Plus; #through;
case .Quest;
newsub := child_args[0];
// Special case: repeat the empty string as much as
// you want, but it's still the empty string.
if newsub.op == .EmptyMatch return newsub;
// These are simple as long as the subpiece is simple.
if newsub == re.subs[0] {
re.simple = true;
return re;
}
// These are also idempotent if flags are constant.
if re.op == newsub.op && re.parse_flags == newsub.parse_flags return newsub;
nre := new_regexp(pool, re.op, re.parse_flags);
nre.subs = NewArray(1, *Regexp_Node, false);
nre.subs[0] = newsub;
nre.simple = true;
return nre;
case .Repeat;
newsub := child_args[0];
// Special case: repeat the empty string as much as
// you want, but it's still the empty string.
if newsub.op == .EmptyMatch return newsub;
nre := simplify_repeat(pool, newsub, re.min, re.max, re.parse_flags);
nre.simple = true;
return nre;
case .CharClass;
nre := simplify_char_class(pool, re);
nre.simple = true;
return nre;
case;
assert(false, "Simpilfy case not handled: %", re.op);
return null;
}
}
w := Walk(*Regexp_Pool, *Regexp_Node).{pre_visit = simplify_pre, post_visit = simplify_post};
result, stopped := walk(pool, re, null, w);
if stopped return null;
return result;
}
// Creates a concatenation of two Regexp_Node, consuming refs to re1 and re2.
// Returns a new Regexp_Node, handing the ref to the caller.
concat2 :: (pool: *Regexp_Pool, re1: *Regexp_Node, re2: *Regexp_Node, parse_flags: ParseFlags) -> *Regexp_Node {
re := new_regexp(pool, .Concat, parse_flags);
re.subs = NewArray(2, *Regexp_Node, false);
re.subs[0] = re1;
re.subs[1] = re2;
return re;
}
// Simplifies the expression re{min,max} in terms of *, +, and ?.
// Returns a new regexp. Does not edit re. Does not consume reference to re.
// Caller must Decref return value when done with it.
// The result will *not* necessarily have the right capturing parens
// if you call ToString() and re-parse it: (x){2} becomes (x)(x),
// but in the Regexp_Node* representation, both (x) are marked as $1.
simplify_repeat :: (pool: *Regexp_Pool, re: *Regexp_Node, min: int, max: int, f: ParseFlags) -> *Regexp_Node {
// x{n,} means at least n matches of x.
if (max == -1) {
// Special case: x{0,} is x*
if (min == 0) return new_star(pool, re, f);
// Special case: x{1,} is x+
if (min == 1) return new_plus(pool, re, f);
// General case: x{4,} is xxxx+
nre_subs := NewArray(min, *Regexp_Node, false);
for i: 0..min-2 {
nre_subs[i] = re;
}
nre_subs[min-1] = new_plus(pool, re, f);
return new_concat(pool, nre_subs, f);
}
// Special case: (x){0} matches only empty string.
if (min == 0 && max == 0) return new_regexp(pool, .EmptyMatch, f);
// Special case: x{1} is just x.
if (min == 1 && max == 1) return re;
// General case: x{n,m} means n copies of x and m copies of x?.
// The machine will do less work if we nest the final m copies,
// so that x{2,5} = xx(x(x(x)?)?)?
// Build leading prefix: xx. Capturing only on the last one.
nre: *Regexp_Node;
if (min > 0) {
nre_subs := NewArray(min, *Regexp_Node, false);
for i: 0..min-1 {
nre_subs[i] = re;
}
nre = new_concat(pool, nre_subs, f);
}
// Build and attach suffix: (x(x(x)?)?)?
if (max > min) {
suf := new_quest(pool, re, f);
for i: min+1..max-1 {
suf = new_quest(pool, concat2(pool, re, suf, f), f);
}
if (nre == null) {
nre = suf;
} else {
nre = concat2(pool, nre, suf, f);
}
}
// Some degenerate case, like min > max, or min < max < 0.
// This shouldn't happen, because the parser rejects such regexps.
assert(nre != null, "Malformed repeat: % %", min, max);
return nre;
}
// Simplifies a character class.
simplify_char_class :: (pool: *Regexp_Pool, re: *Regexp_Node) -> *Regexp_Node {
// Special cases
if (re.char_class.nrunes == 0) return new_regexp(pool, .NoMatch, re.parse_flags);
if (re.char_class.nrunes == Runemax + 1) return new_regexp(pool, .AnyChar, re.parse_flags);
return re;
}
#scope_file
// @ToDo: Move to a common utility module
slice :: inline (array: [] $T, index: int, count: int) -> [] T {
assert(index >= 0, "index = %", index); // @@ Should we also clamp in these cases?
assert(count >= 0, "count = %", count);
c: [] T = ---;
if index >= array.count {
c.data = null;
c.count = 0;
return c;
}
if index + count > array.count {
count = array.count - index;
}
c.data = array.data + index;
c.count = count;
return c;
}