PINSEL3 for LED1-4 on LPC1768

main.c

#define P1_18_SEL (1 << 5) | (1 << 4)   /* Pin 1.18 = LED1 */
#define P1_20_SEL (1 << 9) | (1 << 8)   /* Pin 1.20 = LED2 */ 
#define P1_21_SEL (1 << 11) | (1 << 10) /* Pin 1.21 = LED3 */
#define P1_23_SEL (1 << 15) | (1 << 14) /* Pin 1.23 = LED4 */

...
  
  /* Set the pins to GPIO by setting the associated bits to 00 (p119)
   */
  LPC_PINCON->PINSEL3 &= (unsigned) ~(P1_18_SEL | P1_20_SEL | P1_21_SEL | P1_23_SEL);