[PATCH 57/89] drm/i915: Rewrite ABS_DIFF() in a safer manner

Damien Lespiau
2014-09-04T11:28:52Z

The new version of the macro does a few things better:
- protect the arguments,
- only evaluate the arguments once,
- check that the arguments are of the same type,

Change LC_FREQ_2K to be a unsigned 64bit constant and removed the '()'
from the caller as a result.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
---
drivers/gpu/drm/i915/intel_ddi.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 64eda53..ba1103f 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -460,7 +460,7 @@ intel_ddi_get_crtc_encoder(struct drm_crtc *crtc)
}

#define LC_FREQ 2700
-#define LC_FREQ_2K (LC_FREQ * 2000)
+#define LC_FREQ_2K U64_C(LC_FREQ * 2000)

#define P_MIN 2
#define P_MAX 64
@@ -472,7 +472,11 @@ intel_ddi_get_crtc_encoder(struct drm_crtc *crtc)
#define VCO_MIN 2400
#define VCO_MAX 4800

-#define ABS_DIFF(a, b) ((a > b) ? (a - b) : (b - a))
+#define abs_diff(a, b) ({ \
+ typeof(a) __a = (a); \
+ typeof(b) __b = (b); \
+ (void) (&__a == &__b); \
+ __a > __b ? (__a - __b) : (__b - __a); })

struct wrpll_rnp {
unsigned p, n2, r2;
@@ -582,9 +586,9 @@ static void wrpll_update_rnp(uint64_t freq2k, unsigned budget,
*/
a = freq2k * budget * p * r2;
b = freq2k * budget * best->p * best->r2;
- diff = ABS_DIFF((freq2k * p * r2), (LC_FREQ_2K * n2));
- diff_best = ABS_DIFF((freq2k * best->p * best->r2),
- (LC_FREQ_2K * best->n2));
+ diff = abs_diff(freq2k * p * r2, LC_FREQ_2K * n2);
+ diff_best = abs_diff(freq2k * best->p * best->r2,
+ LC_FREQ_2K * best->n2);
c = 1000000 * diff;
d = 1000000 * diff_best;

--
1.8.3.1