// a:c = a+x+c   c is bool - carry flag
inline void ADC(u64*a, u64 x, u64*c) {
  __asm__("negq %1        ;"
          "adcq %3, %0    ;"
          "sbbq %1, %1    ;"
          : "=rm" (*a), "=r" (*c)
          : "1" (*c), "r" (x)
          : "cc");
}



// zN:-borrow = zN - xN*y - w
// return is borrow
u64 _mulsub_NN1(u64*z, u64*x, u64 y, u64 w, i64 N) {
  assert(N>=0);
  u64 a=0, b=0; // two carry flags
  u64 l, h;
  for (i64 i=0; i<N; i++) {

INT3();

    MUL(&l, &h, x[i], y);
printf("after MUL:\n");
printf("h: %llu \n",h);
printf("b: %llu \n",b);

printf("l: %llu \n",l);
printf("w: %llu \n",w);
printf("a: %llu \n",a);

    ADC(&l, w, &a);

printf("after ADC:\n");
printf("l: %llu \n",l);
printf("w: %llu \n",w);
printf("a: %llu \n",a);


    SBB(&z[i], l, &b);

printf("after SBB:\n");
printf("z[i]: %llu \n",z[i]);
printf("l: %llu \n",l);
printf("b: %llu \n",b);


    w = h;
  }
  ADC(&w, 0, &b);
printf("w: %llu \n",w);
  return w;
}


program output

l: 6      <- these are all correct
w: 0      <- these are all correct
a: 0      <- these are all correct
after ADC:
l: 2357104   <- l should be 6 here, but is actually the address of l
w: 0
a: 0
after SBB:
z[i]: 1773168
l: 2357104
b: 0
w: 2357176
b: 2357176
b: 2357160
Assertion failed!

Program: C:\Users\pc\Dropbox\cas\cas.exe
File: idiv.cpp, Line 268

Expression: b==0

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

C:\Users\pc\Dropbox\cas>