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Annotation of cci/usr/src/lib/libc/tahoe/gen/ldexp.s, revision 1.1

1.1     ! root        1: 
        !             2: /* @(*)ldexp.s 4.2 (Berkeley) 12/21/80
        !             3: *      Tahoe           2/2/83
        !             4: *
        !             5: *      double ldexp (value, exp)
        !             6: *              double value;
        !             7: *              int exp;
        !             8: *
        !             9: *      Ldexp returns value*2**exp, if that result is in range.
        !            10: *      If underflow occurs, it returns zero.  If overflow occurs,
        !            11: *      it returns a value of appropriate sign and largest
        !            12: *      possible magnitude.  In case of either overflow or underflow,
        !            13: *      the external int "errno" is set to ERANGE.  Note that errno is
        !            14: *      not modified if no error occurs, so if you intend to test it
        !            15: *      after you use ldexp, you had better set it to something
        !            16: *      other than ERANGE first (zero is a reasonable value to use).
        !            17: *
        !            18: *      Constants
        !            19: */
        !            20:        .set    erange,34       /* error number for range error */
        !            21: 
        !            22: /*     Constants to be in a flt.h file . (?) */
        !            23: 
        !            24:        .set            EXPMASK,        0x7f800000
        !            25:        .set            SIGNBIT,        0x80000000
        !            26:        .set            EXPSHIFT,       23
        !            27:        .data
        !            28:        .globl  _errno          /* error flag */
        !            29: 
        !            30: huge0: .word   0x7fff          /* The largest number that can */
        !            31:        .word   0xffff          /*   be represented in a long floating */
        !            32: huge1: .word   0xffff          /*   number.  */
        !            33:        .word   0xffff          
        !            34: /*
        !            35: *      Entry point
        !            36: */
        !            37:        .text
        !            38:        .globl  _ldexp
        !            39: _ldexp:        .word   0x0004          /* We use r2  */
        !            40: 
        !            41:        movl    4(fp),r0        /* Fetch "value" */
        !            42:        movl    8(fp),r1        
        !            43: 
        !            44:        andl3   $EXPMASK,r0,r2  /* r2 := shifted biased exponent */
        !            45:        jeql    ld1             /* If it's zero, we're done */
        !            46:        shar    $EXPSHIFT,r2,r2 /* shift to get value of exponent  */
        !            47: 
        !            48:        addl2   12(fp),r2       /* r2 := new biased exponent */
        !            49:        jleq    under           /* if it's <= 0, we have an underflow */
        !            50:        cmpl    r2,$256         /* Otherwise check if it's too big */
        !            51:        jgeq    over            /* jump if overflow */
        !            52: /*
        !            53: *      Construct the result and return
        !            54: */
        !            55:        andl2   $0!EXPMASK,r0   /* clear old exponent */
        !            56:        shal    $EXPSHIFT,r2,r2 /* Put the exponent back in the result */
        !            57:        orl2    r2,r0
        !            58: ld1:   ret
        !            59: /*
        !            60: *      Underflow
        !            61: */
        !            62: under: clrl    r0              /* Result is zero */
        !            63:        clrl    r1
        !            64:        jbr     err             /* Join general error code */
        !            65: /*
        !            66: *      Overflow
        !            67: */
        !            68: over:  movl    huge0,r0        /* Largest possible floating magnitude */
        !            69:        movl    huge1,r1
        !            70:        jbc     $31,4(fp),err   /* Jump if argument was positive */
        !            71:        orl2    $SIGNBIT,r0     /* If arg < 0, make result negative */
        !            72: 
        !            73: err:   movl    $erange,_errno  /* Indicate range error */
        !            74:        ret

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