ref: b2e29cf3158d6e8c6a0263cb1bbb06e72a21f7fb dir: /sys/src/libc/386/387/tan.s/
TEXT tan(SB), $0 FMOVD a+0(FP), F0 FPTAN FMOVDP F0, F0 /* get rid of extra 1.0 */ RET