Bitfields
- Mini structure members.
- Subject to pointer aliasing.
- Layout not guaranteed.
On the whole, you’re better off using a flags word.
Examples
typedef struct {
unsigned int hasLasers : 1;
unsigned int hasMissiles : 1;
unsigned int hasBomb : 1;
unsigned int hasECM : 1;
} ShipData;
ShipFlags getShipFlags(const ShipData *d)
{
return (d->hasLasers << 0) |
(d->hasMissiles << 1) |
(d->hasBomb << 2) |
(d->hasECM << 3);
}
getShipFlags LDR r0,[r0,#0]
AND r0,r0,#0xf
MOV pc,lr
typedef struct {
ShipFlags flags;
} ShipData2;
ShipFlags getShipFlags2(const ShipData2 *d)
{
return d->flags;
}
getShipFlags2 LDR r0,[r0,#0]
MOV pc,lr
