v.scanner: use table lookups for very frequently done character checks (

#21931)

vlib/v/scanner/scanner.v

@@ -239,7 +239,7 @@ fn (mut s Scanner) ident_name() string {
 	s.pos++
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
-		if c.is_alnum() || c == `_` {
+		if util.func_char_table[c] {
 			s.pos++
 			continue
 		}
@@ -537,7 +537,7 @@ fn (mut s Scanner) skip_whitespace() {
 			s.pos++
 			continue
 		}
-		if !(c == 32 || (c > 8 && c < 14) || c == 0x85 || c == 0xa0) {
+		if util.non_whitespace_table[c] {
 			return
 		}
 		c_is_nl := c == scanner.b_cr || c == scanner.b_lf
@@ -686,7 +686,7 @@ pub fn (mut s Scanner) text_scan() token.Token {
 		c := s.text[s.pos]
 		nextc := s.look_ahead(1)
 		// name or keyword
-		if util.is_name_char(c) {
+		if util.name_char_table[c] {
 			name := s.ident_name()
 			// tmp hack to detect . in ${}
 			// Check if not .eof to prevent panic
@@ -1315,7 +1315,7 @@ pub fn (mut s Scanner) ident_string() string {
 			break
 		}
 		// $var
-		if prevc == `$` && util.is_name_char(c) && !is_raw
+		if prevc == `$` && util.name_char_table[c] && !is_raw
 			&& s.count_symbol_before(s.pos - 2, scanner.backslash) & 1 == 0 {
 			s.is_inside_string = true
 			s.is_inter_start = true

vlib/v/util/scanning.v

@@ -1,13 +1,43 @@
 module util
 
-@[inline]
+pub const name_char_table = get_name_char_table()
+
+pub const func_char_table = get_func_char_table()
+
+pub const non_whitespace_table = get_non_white_space_table()
+
+fn get_non_white_space_table() [256]bool {
+	mut bytes := [256]bool{}
+	for c in 0 .. 256 {
+		bytes[c] = !u8(c).is_space()
+	}
+	return bytes
+}
+
+fn get_name_char_table() [256]bool {
+	mut res := [256]bool{}
+	for c in 0 .. 256 {
+		res[c] = u8(c).is_letter() || c == `_`
+	}
+	return res
+}
+
+fn get_func_char_table() [256]bool {
+	mut res := [256]bool{}
+	for c in 0 .. 256 {
+		res[c] = u8(c).is_letter() || u8(c).is_digit() || c == `_`
+	}
+	return res
+}
+
+@[direct_array_access; inline]
 pub fn is_name_char(c u8) bool {
-	return c.is_letter() || c == `_`
+	return util.name_char_table[c]
 }
 
-@[inline]
+@[direct_array_access; inline]
 pub fn is_func_char(c u8) bool {
-	return c.is_letter() || c == `_` || c.is_digit()
+	return util.func_char_table[c]
 }
 
 pub fn contains_capital(s string) bool {