implement non-default plural rules for ngettext translations

the new code in dcngettext was written by me, and the expression
evaluator by Szabolcs Nagy (nsz).

src/locale/dcngettext.c

@@ -4,6 +4,7 @@
 #include <errno.h>
 #include <limits.h>
 #include <sys/stat.h>
+#include <ctype.h>
 #include "locale_impl.h"
 #include "libc.h"
 #include "atomic.h"
@@ -95,6 +96,8 @@ struct msgcat {
 	struct msgcat *next;
 	const void *map;
 	size_t map_size;
+	void *plural_rule;
+	int nplurals;
 	char name[];
 };
 
@@ -107,6 +110,7 @@ weak_alias(dummy_gettextdomain, __gettextdomain);
 
 const unsigned char *__map_file(const char *, size_t *);
 int __munmap(void *, size_t);
+unsigned long __pleval(const char *, unsigned long);
 
 char *dcngettext(const char *domainname, const char *msgid1, const char *msgid2, unsigned long int n, int category)
 {
@@ -190,19 +194,53 @@ notrans:
 	const char *trans = __mo_lookup(p->map, p->map_size, msgid1);
 	if (!trans) goto notrans;
 
-	/* FIXME: support alternate plural rules */
-	if (n != 1) {
-		size_t l = strlen(trans);
-		if (l+1 >= p->map_size - (trans - (char *)p->map))
-			goto notrans;
-		trans += l+1;
+	/* Non-plural-processing gettext forms pass a null pointer as
+	 * msgid2 to request that dcngettext suppress plural processing. */
+	if (!msgid2) return (char *)trans;
+
+	if (!p->plural_rule) {
+		const char *rule = "n!=1;";
+		unsigned long np = 2;
+		const char *r = __mo_lookup(p->map, p->map_size, "");
+		char *z;
+		while (r && strncmp(r, "Plural-Forms:", 13)) {
+			z = strchr(r, '\n');
+			r = z ? z+1 : 0;
+		}
+		if (r) {
+			r += 13;
+			while (isspace(*r)) r++;
+			if (!strncmp(r, "nplurals=", 9)) {
+				np = strtoul(r+9, &z, 10);
+				r = z;
+			}
+			while (*r && *r != ';') r++;
+			if (*r) {
+				r++;
+				while (isspace(*r)) r++;
+				if (!strncmp(r, "plural=", 7))
+					rule = r+7;
+			}
+		}
+		a_store(&p->nplurals, np);
+		a_cas_p(&p->plural_rule, 0, (void *)rule);
+	}
+	if (p->nplurals) {
+		unsigned long plural = __pleval(p->plural_rule, n);
+		if (plural > p->nplurals) goto notrans;
+		while (plural--) {
+			size_t l = strlen(trans);
+			if (l+1 >= p->map_size - (trans - (char *)p->map))
+				goto notrans;
+			trans += l+1;
+		}
 	}
 	return (char *)trans;
 }
 
 char *dcgettext(const char *domainname, const char *msgid, int category)
 {
-	return dcngettext(domainname, msgid, msgid, 1, category);
+	return dcngettext(domainname, msgid, 0, 1, category);
 }
 
 char *dngettext(const char *domainname, const char *msgid1, const char *msgid2, unsigned long int n)
@@ -212,5 +250,5 @@ char *dngettext(const char *domainname, const char *msgid1, const char *msgid2,
 
 char *dgettext(const char *domainname, const char *msgid)
 {
-	return dcngettext(domainname, msgid, msgid, 1, LC_MESSAGES);
+	return dcngettext(domainname, msgid, 0, 1, LC_MESSAGES);
 }

src/locale/pleval.c

@@ -0,0 +1,197 @@
+#include <stdlib.h>
+#include <ctype.h>
+
+/*
+grammar:
+
+Start = Expr ';'
+Expr  = Or | Or '?' Expr ':' Expr
+Or    = And | Or '||' And
+And   = Eq | And '&&' Eq
+Eq    = Rel | Eq '==' Rel | Eq '!=' Rel
+Rel   = Add | Rel '<=' Add | Rel '>=' Add | Rel '<' Add | Rel '>' Add
+Add   = Mul | Add '+' Mul | Add '-' Mul
+Mul   = Term | Mul '*' Term | Mul '/' Term | Mul '%' Term
+Term  = '(' Expr ')' | '!' Term | decimal | 'n'
+
+internals:
+
+recursive descent expression evaluator with stack depth limit.
+eval* functions return the value of the subexpression and set
+the current string pointer to the next non-space char.
+*/
+
+struct st {
+	const char *s;
+	unsigned long n;
+	int err;
+};
+
+static const char *skipspace(const char *s)
+{
+	while (isspace(*s)) s++;
+	return s;
+}
+
+static unsigned long evalconst(struct st *st)
+{
+	char *e;
+	unsigned long n;
+	n = strtoul(st->s, &e, 10);
+	if (!isdigit(*st->s) || e == st->s || n == -1)
+		st->err = 1;
+	st->s = skipspace(e);
+	return n;
+}
+
+static unsigned long evalexpr(struct st *st, int d);
+
+static unsigned long evalterm(struct st *st, int d)
+{
+	unsigned long a;
+	if (d <= 0) {
+		st->err = 1;
+		return 0;
+	}
+	st->s = skipspace(st->s);
+	if (*st->s == '!') {
+		st->s++;
+		return !evalterm(st, d-1);
+	}
+	if (*st->s == '(') {
+		st->s++;
+		a = evalexpr(st, d-1);
+		if (*st->s != ')') {
+			st->err = 1;
+			return 0;
+		}
+		st->s = skipspace(st->s + 1);
+		return a;
+	}
+	if (*st->s == 'n') {
+		st->s = skipspace(st->s + 1);
+		return st->n;
+	}
+	return evalconst(st);
+}
+
+static unsigned long evalmul(struct st *st, int d)
+{
+	unsigned long b, a = evalterm(st, d-1);
+	int op;
+	for (;;) {
+		op = *st->s;
+		if (op != '*' && op != '/' && op != '%')
+			return a;
+		st->s++;
+		b = evalterm(st, d-1);
+		if (op == '*') {
+			a *= b;
+		} else if (!b) {
+			st->err = 1;
+			return 0;
+		} else if (op == '%') {
+			a %= b;
+		} else {
+			a /= b;
+		}
+	}
+}
+
+static unsigned long evaladd(struct st *st, int d)
+{
+	unsigned long a = 0;
+	int add = 1;
+	for (;;) {
+		a += (add?1:-1) * evalmul(st, d-1);
+		if (*st->s != '+' && *st->s != '-')
+			return a;
+		add = *st->s == '+';
+		st->s++;
+	}
+}
+
+static unsigned long evalrel(struct st *st, int d)
+{
+	unsigned long b, a = evaladd(st, d-1);
+	int less, eq;
+	for (;;) {
+		if (*st->s != '<' && *st->s != '>')
+			return a;
+		less = st->s[0] == '<';
+		eq = st->s[1] == '=';
+		st->s += 1 + eq;
+		b = evaladd(st, d-1);
+		a = (less ? a < b : a > b) || (eq && a == b);
+	}
+}
+
+static unsigned long evaleq(struct st *st, int d)
+{
+	unsigned long a = evalrel(st, d-1);
+	int neg;
+	for (;;) {
+		if ((st->s[0] != '=' && st->s[0] != '!') || st->s[1] != '=')
+			return a;
+		neg = st->s[0] == '!';
+		st->s += 2;
+		a = evalrel(st, d-1) == a;
+		a ^= neg;
+	}
+}
+
+static unsigned long evaland(struct st *st, int d)
+{
+	unsigned long a = evaleq(st, d-1);
+	for (;;) {
+		if (st->s[0] != '&' || st->s[1] != '&')
+			return a;
+		st->s += 2;
+		a = evaleq(st, d-1) && a;
+	}
+}
+
+static unsigned long evalor(struct st *st, int d)
+{
+	unsigned long a = evaland(st, d-1);
+	for (;;) {
+		if (st->s[0] != '|' || st->s[1] != '|')
+			return a;
+		st->s += 2;
+		a = evaland(st, d-1) || a;
+	}
+}
+
+static unsigned long evalexpr(struct st *st, int d)
+{
+	unsigned long a1, a2, a3;
+	if (d <= 0) {
+		st->err = 1;
+		return 0;
+	}
+	a1 = evalor(st, d-1);
+	if (*st->s != '?')
+		return a1;
+	st->s++;
+	a2 = evalexpr(st, d-1);
+	if (*st->s != ':') {
+		st->err = 1;
+		return 0;
+	}
+	st->s++;
+	a3 = evalexpr(st, d-1);
+	return a1 ? a2 : a3;
+}
+
+unsigned long __pleval(const char *s, unsigned long n)
+{
+	unsigned long a;
+	struct st st;
+	st.s = s;
+	st.n = n;
+	st.err = 0;
+	a = evalexpr(&st, 100);
+	if (st.err || *st.s != ';')
+		return -1;
+	return a;
+}