From ce05175372a9ddca1a225db0765ace1127a39293 Mon Sep 17 00:00:00 2001
From: Nicholas <nbnoll@eml.cc>
Date: Fri, 12 Nov 2021 09:22:01 -0800
Subject: chore: simplified organizational structure

---
 src/libsre/lex.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 246 insertions(+)
 create mode 100644 src/libsre/lex.c

(limited to 'src/libsre/lex.c')

diff --git a/src/libsre/lex.c b/src/libsre/lex.c
new file mode 100644
index 0000000..f4c6ac2
--- /dev/null
+++ b/src/libsre/lex.c
@@ -0,0 +1,246 @@
+#include "sre.h"
+
+static
+State *
+state(Machine *m, int t)
+{
+    if (m->state >= m->statestk + arrlen(m->statestk))
+        panicf("regexp vm: out of state space");
+
+    m->state->type = t;
+    m->state->l = nil;
+    m->state->r = nil;
+    
+    return m->state++;
+}
+
+static
+int
+poptor(Parser *p)
+{
+    if (p->optor <= p->optorstk) 
+        panicf("regexp parser: opand stack underflow");
+
+    return *--p->optor;
+}
+
+static
+void
+pushtor(Parser *p, int t)
+{
+    if (p->optor >= arrend(p->optorstk))
+        panicf("regexp parser: opand stack overflow");
+
+    *p->optor++ = t;
+}
+
+static
+void
+pushand(Parser *p, State *beg, State *end)
+{
+    if (p->node >= arrend(p->nodestk))
+        panicf("regexp parser: opand stack overflow");
+
+    p->node->beg = beg;
+    p->node->end = end;
+
+    p->node++;
+}
+
+static
+Node *
+popand(Parser *p)
+{
+    if (p->node <= p->nodestk)
+        panicf("regexp parser: opand stack underflow");
+
+    return --p->node;
+}
+
+static
+void
+operateuntil(Parser *p, int prec)
+{
+    Node  *o1, *o2, *t;
+    State *s1, *s2;
+
+    while (prec == Trparen || p->optor[-1] >= prec) {
+        switch (poptor(p)) {
+        case Tor:
+            o1 = popand(p);
+            o2 = popand(p);
+
+            s1 = state(p->mach, Tor);
+            s2 = state(p->mach, Tnop);
+            s1->l = o1->beg;
+            s1->r = o2->beg;
+
+            o1->end->out = s2;
+            o2->end->out = s2;
+
+            pushand(p, s1, s2);
+            break;
+
+        case Tcat:
+            o1 = popand(p);
+            o2 = popand(p);
+
+            o1->end->out = o2->beg;
+            pushand(p, o1->beg, o2->end);
+            break;
+
+        case Tstar:
+            o1 = popand(p);
+            s1 = state(p->mach, Tor);
+            o1->end->out = s1;
+            s1->l = o1->beg;
+            pushand(p, s1, s1);
+            break;
+
+        case Tplus:
+            o1 = popand(p);
+            s1 = state(p->mach, Tor);
+            o1->end->out = s1;
+            s1->l = o1->beg;
+            pushand(p, o1->beg, s1);
+            break;
+
+        case Tqmark:
+            o1 = popand(p);
+            s1 = state(p->mach, Tor);
+            s2 = state(p->mach, Tnop);
+            s1->l = o1->beg;
+            s1->r = s2;
+            o1->end->out = s2;
+            pushand(p, s1, s2);
+            break;
+
+        default:
+            panicf("unsupported regexp operator");
+        }
+    }
+}
+
+static
+void
+operator(Parser *p, int t)
+{
+    operateuntil(p, t);
+    pushtor(p, t);
+    p->wasopand = (t != Tstar && t != Tqmark && t != Tplus && t != Trparen);
+}
+
+static
+void
+operand(Parser *p, int t)
+{
+    State *new;
+    if (p->wasopand)
+        operator(p, Tcat);
+    
+    new = state(p->mach, t);
+    pushand(p, new, new);
+    p->wasopand = true;
+}
+
+#define cinc 20
+int
+lex(Parser *p)
+{
+    int  c, t;
+    byte *class;
+    long n, cap;
+
+    c = *p->re++;
+    switch (c) {
+    case '\\':
+        if (*p->re)
+            if ((c = *p->re++) == '\n')
+                c = '\n';
+        break;
+    case '\0':
+        c = Tend,
+        --p->re;
+        break;
+    case '*':
+        c = Tstar;
+        break;
+    case '?':
+        c = Tqmark;
+        break;
+    case '+':
+        c = Tplus;
+        break;
+    case '|':
+        c = Tor;
+        break;
+    case '.':
+        c = Tany;
+        break;
+    case '(':
+        c = Tlparen;
+        break;
+    case ')':
+        c = Trparen;
+        break;
+    case '^':
+        c = Tbol;
+        break;
+    case '$':
+        c = Teol;
+        break;
+    case '[':
+        goto charclass;
+    default: 
+        ;
+    }
+    return c;
+
+charclass:
+    panicf("to implement");
+}
+
+#undef cinc
+
+static
+State*
+optimize(State *entry)
+{
+    State *curr, *next;
+    for (curr=entry; curr->type != Tend; curr++) {
+        next = curr->out;
+        while (next->type == Tnop) 
+            next = next->out;
+        curr->out = next;
+    }
+
+    return entry;
+}
+
+void
+sre·compile(Machine *mach, byte *regexp)
+{
+    int  tok;
+    Parser p;
+    Node  *prog;
+
+    p = (Parser) {
+        .re   = regexp,
+        .mach = mach,
+        .node = p.nodestk,
+    };
+
+    pushtor(&p, Tstart - 1);
+    while ((tok = lex(&p)) != Tend) {
+        if ((tok & isoptor) == Toperator)
+            operator(&p, tok);
+        else
+            operand(&p, tok);
+    }
+    operateuntil(&p, Tstart);
+    operand(&p, Tend);
+    operateuntil(&p, Tstart);
+
+    prog = popand(&p);
+    mach->entry = optimize(prog->beg);
+}
-- 
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