ref: 2c1dc1aa4f374f5c8d6a13e7e82a26c4e27e6775 dir: /sys/src/libc/386/387/atan2.s/
TEXT atan2(SB), $0 FMOVD a+0(FP), F0 FMOVD b+8(FP), F0 FPATAN RET