ref: 65bd53b9b89b0a84d0f16db4adc3f53fa6ab3a3a dir: /sys/src/libc/386/387/atan2.s/
TEXT atan2(SB), $0 FMOVD a+0(FP), F0 FMOVD b+8(FP), F0 FPATAN RET