ref: 0231537cbac846087f5ac132aba5c97ec9d4cffa dir: /sys/src/libc/arm64/floor.s/
TEXT floor(SB), $0 FMOVD x+0(FP), F0 FRINTMD F0, F0 RETURN TEXT ceil(SB), $0 FMOVD x+0(FP), F0 FRINTPD F0, F0 RETURN