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#include "tests/asm.h"
#include <stdio.h>
/* Test whether a shift by zero properly preserves the CC_NDEP thunk. */
/* Check whether the carry flag is properly preserved by a variable
shift when the shift amount happens to be zero. */
int shift_ndep( void )
{
char shift_amt = 0;
int x = -2;
/* First we set the carry flag. Then we increment %x, which sets
CC_OP to X86G_CC_OP_INCL and stores the carry (1) in
CC_NDEP. Then we left shift %x by a variable amount that happens
to be zero, which should leave both %x and all the flags
unchanged. Then we add-with-carry 0 to %x, which (assuming the
carry is still set as it should be) increments %x again. Thus the
expected final value for x is -2 + 1 + 1 = 0.
If instead the shift clears CC_NDEP (as it would legally do if
the shift amount were non-zero), this will be interpeted as
clearing the carry bit, so the adc will be a no-op and the final
value of %x will instead be -1.
*/
asm (
"stc" "\n\t"
"inc %[x]" "\n\t"
"shl %[shift_amt], %[x]" "\n\t"
"adc $0, %[x]" "\n\t"
: [x] "+r" (x) : [shift_amt] "c" (shift_amt));
return x;
}
int main ( void )
{
int r = shift_ndep();
if (r == 0)
printf("Passed (%d).\n", r);
else
printf("Failed (%d).\n", r);
return 0;
}
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