int prob$259($int x$,$ int y$)\{$

return $($y & ~$0$xFF$)|($x & $0$xFF$)$;

$\}$

unsigned replace$\_$byte$($unsigned x$,$ int i$,$ unsigned char b$)\{$

unsigned mask $=0$xFF $<<($i $*8)$;

return $($x & ~mask$)|($b $<<($i $*8))$;

$\}$

int prob$261$A$($int x$)\{$

return $($x & $0$xFF$)==0$xFF;

$\}$

int prob$261$B$($int x$)\{$

return $($x & $0$xFF$000000)==0$;

$\}$

int prob$261$C$($int x$)\{$

return $($x & $0$x$00$FFFFFF$)==0$x$00$FFFFFF;

$\}$

int leftmost$\_$one$($unsigned x$)\{$

x $|=$ x $>>1$;

x $|=$ x $>>2$;

x $|=$ x $>>4$;

x $|=$ x $>>8$;

x $|=$ x $>>16$;

return x & ~$($x $>>1)$;

$\}$

int lower$\_$one$\_$mask$($int n$)\{$

int mask $=(1<<($n $-1))-1$;

return mask $|($mask $+1)$;

$\}$

int main$()\{$

$//$ problem $2\mathrm{.}59$

printf$("$

Problem $2\mathrm{.}59$:

$")$;

int x $=0$x$89$ABCDEF;

int y $=0$x$76543210$;

printf$("0$x$\%$X

$",$ prob$259($x$,$ y$))$;

$//$ problem $2\mathrm{.}60$

printf$("$

Problem $2\mathrm{.}60$:

$")$;

printf$("0$x$\%$X

$",$ replace$\_$byte$(0$x$12345678,2,0$xAB$))$;

printf$("0$x$\%$X

$",$ replace$\_$byte$(0$x$12345678,0,0$xAB$))$;

$//$ problem $2\mathrm{.}61$

printf$("$

Problem $2\mathrm{.}61$:

$")$;

printf$("\%$d

$",$ prob$261$A$(0$x$8))$; $//$ returns $1$

printf$("\%$d

$",$ prob$261$B$(-1))$; $//$ returns $0$

printf$("\%$d

$",$ prob$261$C$(0$x$100))$; $//$ returns $0$

$//$ problem $2\mathrm{.}66$