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Annotation of 43BSDTahoe/sys/tahoemath/Kldexpf.s, revision 1.1.1.1

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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