ref: 7cb2db12f85c6dbc6a7f36bbfb655e6b7c19a28c 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