I use always "dingoo.h" .
It's origin was in "snes9x-sdl for dingux source-code" , and I replaced the numbers to SDLK-defined words.
"DINGOO_BUTTON_END" means PowerSwitch, but it's a little strange.
dingoo.h
#define DINGOO_BUTTON_UP SDLK_UP
#define DINGOO_BUTTON_DOWN SDLK_DOWN
#define DINGOO_BUTTON_RIGHT SDLK_RIGHT
#define DINGOO_BUTTON_LEFT SDLK_LEFT
#define DINGOO_BUTTON_R SDLK_BACKSPACE
#define DINGOO_BUTTON_L SDLK_TAB
#define DINGOO_BUTTON_A SDLK_LCTRL
#define DINGOO_BUTTON_B SDLK_LALT
#define DINGOO_BUTTON_X SDLK_SPACE
#define DINGOO_BUTTON_Y SDLK_LSHIFT
#define DINGOO_BUTTON_SELECT SDLK_ESCAPE
#define DINGOO_BUTTON_START SDLK_RETURN
#define DINGOO_BUTTON_END SDLK_UNKNOWN