void
ReadFileEx(self, hFile, opBuffer, uBytes, uqwOffset, uAlign=0)
    HV * self
    HANDLE hFile
    SV * opBuffer
    unsigned long uBytes
    unsigned __int64 uqwOffset
    unsigned long uAlign
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PREINIT:
    char * opBufferPtr;
    BOOL ret;
    unsigned long alignRemainder;
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CODE:
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    //idea is to avoid a sv_grow and a sv_chop if current SvPVX meets alignment and len requirements
    //SvPVX may already be aligned from a previous ReadFileEx
    if( SvTYPE(opBuffer) < SVt_PV) {                goto grow;}     //svpvx cant be used unless sv type >= pv 
    else if( ! (opBufferPtr = SvPVX(opBuffer))){    goto growPV;}
    else if(uAlign){
        alignRemainder = (DWORD_PTR)opBufferPtr % uAlign;  //opBufferPtr and uAlign can't be 0 here
        //test uBytes+offset to align multiple for current PVX, uBytes+uAlign only needed for a re/malloc op
        //since the alignment of the returned alloc block is assumed to be 0 thru uAlign
        if(alignRemainder && ! (SvLEN(opBuffer) > uBytes + (uAlign-alignRemainder))){ 
            goto growPV;
        } // PVX is already aligned, check alloc len
        else {      goto testLen;}
    }
    testLen:
    if(SvLEN(opBuffer) <= uBytes) {                 goto growPV;}
    if(0){
        growPV: //only if PV, access vio, prevent needless copy in sv_grow 
        SvCUR(opBuffer) = 0; 
        grow: //always include full alignment here, we can't predict alignment of realloced ptr
        opBufferPtr = sv_grow(opBuffer, uBytes+1+uAlign);
    } //offset to next align bouindary must be recacled, opBufferPtr may have changed from 1st align calc
    if(uAlign && (alignRemainder = (DWORD_PTR)opBufferPtr % uAlign)) {
        char * newptr = opBufferPtr = opBufferPtr+(uAlign-alignRemainder);
        //any alignment, any odd number, any even number, any number, not just power of 2, rope to hang yourself
        //(alignRemainder && 1) is a cancel part, so ptr 26 on align 13 doesn't become 39 (26+13) needlessly
        assert(newptr + uBytes < SvPVX(opBuffer) + SvLEN(opBuffer));
        SvPOK_on(opBuffer);
        sv_chop(opBuffer,newptr); //there is an assumption that sv_chop will not realloc since PVX is long enough
        assert(opBufferPtr == SvPVX(opBuffer));
    }
    assert(uAlign?((DWORD_PTR)SvPVX(opBuffer) % uAlign == 0) :1);
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