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Annotation of coherent/b/lib/libm/i387/log87.s, revision 1.1

1.1     ! root        1: //////////
        !             2: / /usr/src/libm/i387/log87.s
        !             3: / i387 mathematics library
        !             4: / log(x), log10(x), ylog2x
        !             5: //////////
        !             6: 
        !             7: RASIZE =       4
        !             8: 
        !             9:        .globl  log10
        !            10:        .globl  log
        !            11:        .globl  _ylog2x
        !            12: /      .globl  _cfcc
        !            13:        .globl  _tstcc
        !            14:        .globl  _edomain
        !            15: 
        !            16: //////////
        !            17: / double
        !            18: / log(x)
        !            19: / double x;
        !            20: /
        !            21: / double
        !            22: / log10(x)
        !            23: / double x;
        !            24: /
        !            25: / ylog2x does the work for log functions and pow().
        !            26: / Passed args x, y on the NDP stack,
        !            27: / it pops both and returns y * log base 2 of x on the NDP stacktop %st.
        !            28: /
        !            29: / Useful identity:
        !            30: /       log base n of x = log base n of 2 * log base 2 of x.
        !            31: / Uses fyl2x, which requires x > 0.
        !            32: //////////
        !            33: 
        !            34: x      =       RASIZE          / arg offset
        !            35: 
        !            36: log10:
        !            37:        fldlg2                  / Load y = log base 10 of 2.
        !            38:        jmp     .L1
        !            39: 
        !            40: log:
        !            41:        fldln2                  / Load y = log base e of 2.
        !            42: 
        !            43: .L1:
        !            44:        fldl    x(%esp)         / Load argument x.
        !            45: 
        !            46: _ylog2x:                       / x, y
        !            47:        call    _tstcc          / Check sign of x.
        !            48:        ja      ?2              / x > 0., ok.
        !            49:        fstp    %st             / x <= 0, pop y.
        !            50:        jmp     _edomain        / Issue EDOM error and return 0.
        !            51: 
        !            52: ?2:
        !            53: //////////
        !            54: / The code below uses
        !            55: /      fyl2x   if d <= 1 or d >= 2-sqrt(2)/2,
        !            56: /      fyl2xp1 if 1 < d < 2-sqrt(2)/2.
        !            57: / Since the precision fyl2xp1 purports to save is already lost,
        !            58: / this appears to make no difference in the result.
        !            59: / The code is commented out for now and should be removed eventually.
        !            60: /      fdcom   near1
        !            61: /      call    _cfcc           / Compare d to 2+sqrt(2)/2.
        !            62: /      jae     ?4              / d >= 2+sqrt(2)/2, use fyl2x.
        !            63: /      fld1                    / Load 1.
        !            64: /      fcom
        !            65: /      call    _cfcc           / Compare 1 to d.
        !            66: /      jae     ?3              / 1 >= d, use fyl2x.
        !            67: /      fsub                    / d = d-1 and pop off the 1.
        !            68: /      fyl2xp1                 / result = y * log base 2 of d+1.
        !            69: /      ret
        !            70: /
        !            71: /?3:   fstp    %st             / Pop off the 1.
        !            72: /
        !            73: /?4:
        !            74: //////////
        !            75:        fyl2x                   / result = y * log base 2 of x.
        !            76:        ret
        !            77: 
        !            78: //////////
        !            79: / Commented out as above...
        !            80: /near?1:       .byte   0x1A, 0x62, 0xC0, 0xCC, 0xB0, 0xAF, 0xF4, 0x3F  / 2 - sqrt(2)/2
        !            81: //////////
        !            82: 
        !            83: / end of log87.s

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