ref: 4dbb99f478d68eaeea4c043a839454cb807c2c7d 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