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Annotation of coherent/b/lib/libc/crt/i386/ducvt.s, revision 1.1

1.1     ! root        1: //////////
        !             2: / libc/crt/i386/ducvt.s
        !             3: / i386 C runtime library.
        !             4: / IEEE software floating point support.
        !             5: //////////
        !             6: 
        !             7: //////////
        !             8: / double _ducvt()
        !             9: / Convert unsigned int in %eax to double, return in %edx:%eax.
        !            10: /
        !            11: / There is no 32-bit shift, so the code below uses an n-1 bit shift
        !            12: / followed by a 1 bit shift rather than an n-bit shift;
        !            13: / this gets (double)1 right without a special case.
        !            14: //////////
        !            15: 
        !            16: BIAS   .equ    1023
        !            17: 
        !            18:        .globl  _ducvt
        !            19: 
        !            20: _ducvt:
        !            21:        bsrl    %edx, %eax              / high bit position 0-31 to EDX (DL)
        !            22:        jz      ?zero                   / return 0.0
        !            23:        push    %ecx
        !            24:        movb    %cl, $31
        !            25:        subb    %cl, %dl                / shift count - 1 to CL
        !            26:        shll    %eax, %cl               / high bit lands at bit 31
        !            27:        shll    %eax, $1                / hidden bit into CF
        !            28:        movl    %ecx, %edx
        !            29:        addl    %ecx, $BIAS             / biased exponent to ECX
        !            30:        shll    %ecx, $20               / position biased exponent
        !            31:        movl    %edx, %eax
        !            32:        shrl    %edx, $12               / hi manissa to EDX
        !            33:        shll    %eax, $20               / lo mantissa to EAX
        !            34:        orl     %edx, %ecx              / exponent
        !            35:        pop     %ecx
        !            36:        ret
        !            37: 
        !            38: ?zero:
        !            39:        sub     %edx, %edx
        !            40:        ret
        !            41: 
        !            42: / end of libc/crt/i386/ducvt.s

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