ref: fe53c0930e8595a2e8b5aa71e907a1f2bec6059b 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