qmk_firmware/keyboards/splitish/splitish.h

#include "quantum.h"

#define LAYOUT( \
    K00, K01, K02, K03, K04, K05,    K06, K07, K08, K09, K0A, K0B, \
    K10, K11, K12, K13, K14, K15,    K16, K17, K18, K19, K1A, K1B, \
    K20, K21, K22, K23, K24, K25,    K26, K27, K28, K29, K2A, K2B, \
    K30, K31, K32, K33, K34, K35,    K36, K37, K38, K39, K3A, K3B  \
) \
{ \
    {K00, K01, K02, K03, K04, K05,    K06, K07, K08, K09, K0A, K0B}, \
    {K10, K11, K12, K13, K14, K15,    K16, K17, K18, K19, K1A, K1B}, \
    {K20, K21, K22, K23, K24, K25,    K26, K27, K28, K29, K2A, K2B}, \
    {K30, K31, K32, K33, K34, K35,    K36, K37, K38, K39, K3A, K3B} \
}