diff --git a/src/stdio/scanf/scan.c b/src/stdio/scanf/scan.c
index 15673a2..82192fc 100644
--- a/src/stdio/scanf/scan.c
+++ b/src/stdio/scanf/scan.c
@@ -2,6 +2,7 @@
 #include "../../stdlib/stdlib_p.h"
 #include <stdio.h>
 #include <ctype.h>
+#include <string.h>
 #include <stdbool.h>
 
 void __scanf_start(struct __scanf_input *in)
@@ -106,50 +107,44 @@ void __scanf_store_d(long double value, int size, va_list *args)
 // %ms and %m[set] are not implemented (with memory allocation while parsing a chain or a set of characters)
 
 
-/* list of allowed char given by a set %[], this is updated at every set */
-bool __asciiallowed[256] = { true };
+/* Set of bytes allowed in a given set %[]. */
+static uint8_t bracket_set[32];
 
-/* unallow all the char for the current set */
-void __unallow_all_set( void )
+/* Allow/disallow the entire set */
+static void bracket_set_init(bool allow)
 {
-	for(int u =0; u<=255; u++)
-		__asciiallowed[u]=false;
+	memset(bracket_set, allow ? 0xff : 0x00, sizeof bracket_set);
 }
 
-/* allow all the char for the current set */
-void __allow_all_set( void )
+/* Allow/disallow a range of characters. Both ends are included. */
+static void bracket_set_range(uint8_t start, uint8_t end, bool allow)
 {
-	for(int u =0; u<=255; u++)
-		__asciiallowed[u]=true;
+	for(int u = start; u <= end; u++) {
+		int byte = u >> 3;
+		int bit = 1 << (u & 7);
+		if(allow)
+			bracket_set[byte] |= bit;
+		else
+			bracket_set[byte] &= ~bit;
+	}
 }
 
-/* allo a range of char for the current set */
-/* note1 : c1 and c2 do not to be sorted */
-/* note2 : not sur if C standard requires to be ordered or not */
-void __define_set_range( char c1, char c2, bool value )
+/* Check whether a byte is allowed by the bracket set. */
+static bool bracket_set_test(int c)
 {
-	char beg = (c1 < c2 ? c1 : c2 );
-	char end = (c1 >= c2 ? c1 : c2 );
-	
-	for (int u=beg; u<=end; u++)
-		__asciiallowed[u] = value;
+	int byte = (c >> 3);
+	int bit = 1 << (c & 7);
+	return (c != EOF) && (bracket_set[byte] & bit);
 }
 
-/* return true if the char is in the allowed set or false otherwise */
-bool __is_allowed(int c)
-{
-	return (c != EOF) && __asciiallowed[c];
-}
-
-
 /* return 0 if Ok or -1 if syntax err in the set format */
-int __scanset(char const * __restrict__ format, int *pos )
+static int bracket_set_parse(char const * __restrict__ format, int *pos )
 {
 	int __sor = 0;
 	int __eor = 0;
 	bool __neg = false;
 
-	__unallow_all_set();
+	bracket_set_init(false);
 
 	(*pos)++;
 	
@@ -157,11 +152,11 @@ int __scanset(char const * __restrict__ format, int *pos )
 	if (format[*pos] == '^' ) {
 		__neg = true;
 		(*pos)++;
-		__allow_all_set();
+		bracket_set_init(true);
 		
 		// the char ']' is part of the set
 		if (format[*pos] == ']' ) {
-			__asciiallowed[ ']' ] = !__neg;
+			bracket_set_range(']', ']', !__neg);
 			(*pos)++;
 		}
 	}
@@ -170,7 +165,7 @@ int __scanset(char const * __restrict__ format, int *pos )
 		__neg = false;
 		// the char ']' is part of the set
 		if (format[*pos] == ']' ) {
-			__asciiallowed[ ']' ] = !__neg;
+			bracket_set_range(']', ']', !__neg);
 			(*pos)++;
 		}
 	}
@@ -180,7 +175,7 @@ int __scanset(char const * __restrict__ format, int *pos )
 		if (format[*pos]=='-') {
 			// the char '-' is included in the allowed set
 			if (format[*pos+1]==']') {
-				__asciiallowed[ '-' ] = !__neg;	// if set in very final position before']', this is the char '-' only
+				bracket_set_range('-', '-', !__neg);
 				(*pos)++;
 				// we have now finished the reading of the set cause the following char is ']'
 				return 0;
@@ -189,7 +184,7 @@ int __scanset(char const * __restrict__ format, int *pos )
 			else {
 				(*pos)++;
 				__eor = format[*pos];
-				__define_set_range( __sor, __eor, !__neg );
+				bracket_set_range( __sor, __eor, !__neg );
 			}
 		}
 		// we find the char ']' so it means we reach the end of this set
@@ -199,7 +194,7 @@ int __scanset(char const * __restrict__ format, int *pos )
 		// we are considering one particular char and prepare for a potential range if we find the char '-' later on
 		else {
 			__sor = format[*pos];
-			__asciiallowed[ __sor ] = !__neg;
+			bracket_set_range(__sor, __sor, !__neg);
 			(*pos)++;
 		}
 	}
@@ -232,8 +227,6 @@ int __scanf(
 		MOD = sizeof(int);
 		skip = false;
 
-		__allow_all_set();
-		
 		if( format[pos] == ' ' ) {
 			__purge_space(in);
 		}
@@ -251,14 +244,14 @@ int __scanf(
 			switch(format[pos]) {
 			// we need to decrypt the corresponding scanf set of character
 			case '[': {
-				err = __scanset( format, &pos );
+				err = bracket_set_parse( format, &pos );
 				if (err!=0) return validrets;
 				int currentlength = 0;
 				// we need to assign the read char to the corresponding pointer
 				char *c = skip ? NULL : va_arg(*args, char *);
 				for(int u=0; u<readmaxlength; u++) {
 					int temp = __scanf_peek(in);
-					if(__is_allowed(temp)) {
+					if(bracket_set_test(temp)) {
 						__scanf_in(in);
 						if(c) *c++ = temp;
 						currentlength++;