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Annotation of 43BSDTahoe/sys/tahoemath/Kldexpf.s, revision 1.1

1.1     ! root        1: /*     Kldexpf.s       1.3     86/01/05        */
        !             2: 
        !             3: #include "../tahoe/SYS.h"
        !             4: #include "../tahoemath/fp.h"
        !             5: #include "../tahoemath/Kfp.h"
        !             6: 
        !             7: /* @(*)Kldexpf.s       4.2 (Berkeley) 12/21/80
        !             8:  *     Tahoe           2/2/83
        !             9:  *
        !            10:  * float Kldexpf (op_most, op_least, exp, hfs)
        !            11:  *
        !            12:  * Ldexp returns value*2**exp, if that result is in range.
        !            13:  * If underflow occurs, it returns zero.  If overflow occurs,
        !            14:  * it returns a value of appropriate sign and largest
        !            15:  * possible magnitude.  In case of either overflow or underflow,
        !            16:  * the external int "errno" is set to ERANGE.  Note that errno is
        !            17:  * not modified if no error occurs, so if you intend to test it
        !            18:  * after you use Kldexpf, you had better set it to something
        !            19:  * other than ERANGE first (zero is a reasonable value to use).
        !            20:  */
        !            21: 
        !            22:        .text
        !            23: ENTRY(Kldexpf, R2)
        !            24:        movl    4(fp),r0        /* Fetch "value" */
        !            25:        movl    8(fp),r1
        !            26: 
        !            27:        andl3   $EXPMASK,r0,r2  /* r2 := shifted biased exponent */
        !            28:        jeql    ld1             /* If it's zero, we're done */
        !            29:        shar    $EXPSHIFT,r2,r2 /* shift to get value of exponent  */
        !            30: 
        !            31:        addl2   12(fp),r2       /* r2 := new biased exponent */
        !            32:        jleq    under           /* if it's <= 0, we have an underflow */
        !            33:        cmpl    r2,$256         /* Otherwise check if it's too big */
        !            34:        jgeq    over            /* jump if overflow */
        !            35: /*
        !            36:  *     Construct the result and return
        !            37:  */
        !            38:        andl2   $0!EXPMASK,r0   /* clear old exponent */
        !            39:        shal    $EXPSHIFT,r2,r2 /* Put the exponent back in the result */
        !            40:        orl2    r2,r0
        !            41: ld1:   ret
        !            42: /*
        !            43:  *     Underflow
        !            44:  */
        !            45: under: clrl    r0              /* Result is zero */
        !            46:        clrl    r1
        !            47:        orl2    $HFS_UNDF,*16(fp)
        !            48:        jmp     err             /* Join general error code */
        !            49: /*
        !            50:  *     Overflow
        !            51:  */
        !            52: over:  movl    huge0,r0        /* Largest possible floating magnitude */
        !            53:        movl    huge1,r1
        !            54:        orl2    $HFS_OVF,*16(fp)
        !            55:        orl2    $SIGNBIT,r0     /* If arg < 0, make result negative */
        !            56: 
        !            57: err:   orl2    $HFS_RANGE,*16(fp)      /* Indicate range error */
        !            58:        ret
        !            59: 
        !            60:        .data
        !            61: huge0: .long   0x7fffffff
        !            62: huge1: .long   0xffffffff

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