int (*dxt5ys_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
int (*rgtc1s_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
int (*rgtc1u_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
+ int (*rgtc1u_gray_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
int (*rgtc1u_alpha_block)(uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
int (*rgtc2s_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
int (*rgtc2u_block) (uint8_t *dst, ptrdiff_t stride, const uint8_t *block);