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

1.1       root        1: /*     Kcvtlf.s        1.3     86/01/05        */
                      2: 
                      3: #include "../tahoemath/fp.h"
                      4: #include "../tahoemath/Kfp.h"
                      5: #include "../tahoe/SYS.h"
                      6: 
                      7:        .text
                      8: ENTRY(Kcvtlf, R5|R4|R3|R2)
                      9:        clrl    r1
                     10:        clrl    r4              # r4 - negative flag.
                     11:        clrl    r2              # r2 - exponent.
                     12:        movl    12(fp),r0       # fetch operand.
                     13:        movl    r0,r5           # need another copy.
                     14:        jeql    retzero         # return zero.
                     15:        jgtr    positive
                     16:        mnegl   r0,r0
                     17:        jvs     retmin          # return minimum integer.
                     18:        incl    r4              # remember it was negative.
                     19:        movl    r0,r5           # remember the negated value.
                     20:  #
                     21:  #Compute exponent:
                     22:  #
                     23: positive:
                     24:        ffs     r0,r1
                     25:        incl    r1
                     26:        addl2   r1,r2
                     27:        shrl    r1,r0,r0
                     28:        jneq    positive        # look for more set bits.
                     29:  #
                     30:  #we have the exponent in r2.
                     31:  #
                     32:        movl    r5,r0           # r0 will hold the resulting f.p. number.
                     33:  #
                     34:  #Shift the fraction part to its proper place:
                     35:  #
                     36:        subl3   r2,$HID_POS,r3
                     37:        jlss    shiftr          # if less then zero we have to shift right.
                     38:        shll    r3,r0,r0        # else we shift left.
                     39:        jmp     shifted
                     40: shiftr:
                     41:        mnegl   r3,r3
                     42:        shrl    r3,r0,r0
                     43: shifted:
                     44:        andl2   $CLEARHID,r0    # clear the hidden bit.
                     45:        shal    $EXPSHIFT,r2,r2 # shift the exponent to its proper place.
                     46:        orl2    $EXPSIGN,r2     # set the exponent sign bit(to bias it).
                     47:        orl2    r2,r0           # combine exponent & fraction.
                     48:        bbc     $0,r4,sign_ok   # do we  have to set the sign bit?
                     49:        orl2    $SIGNBIT,r0     # yes...
                     50: sign_ok:
                     51:        ret
                     52: 
                     53: retzero:
                     54:        clrl    r0
                     55:        ret
                     56: 
                     57: retmin:
                     58:        movl    $0xd0000000,r0
                     59:        ret

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