format/fxt1: Clean up fxt1_variance's argument list

gcc 11 warns:

../src/util/format/u_format_fxt1.c:940:22: warning: ‘fxt1_variance.constprop’ accessing 128 bytes in a region of size 64 [-Wstringop-overflow=]
  940 |    int32_t maxVarR = fxt1_variance(NULL, &input[N_TEXELS / 2], n_comp);

But, suspiciously, if you inline fxt1_variance the warning goes away.
What's happening is that the 2nd arg is uint8_t[N_TEXELS][MAX_COMP], so
it looks like we're passing too small of an array in since gcc knows
that `input` is also [N_TEXELS][MAX_COMP]. Fair enough. Fix the
signature to reflect what's actually going on, and remove some unused
arguments while we're at it.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10671>

diff --git a/src/util/format/u_format_fxt1.c b/src/util/format/u_format_fxt1.c
index 1beee16..e1d9308 100644 (file)
--- a/src/util/format/u_format_fxt1.c
+++ b/src/util/format/u_format_fxt1.c
@@ -189,9 +189,9 @@ fxt1_worst (float vec[MAX_COMP],
 
 
 static int32_t
-fxt1_variance (double variance[MAX_COMP],
-               uint8_t input[N_TEXELS][MAX_COMP], int32_t nc, int32_t n)
+fxt1_variance (uint8_t input[N_TEXELS / 2][MAX_COMP], int32_t nc)
 {
+   const int n = N_TEXELS / 2;
    int32_t i, k, best = 0;
    int32_t sx, sx2;
    double var, maxvar = -1; /* small enough */
@@ -209,9 +209,6 @@ fxt1_variance (double variance[MAX_COMP],
          maxvar = var;
          best = i;
       }
-      if (variance) {
-         variance[i] = var;
-      }
    }
 
    return best;
@@ -935,8 +932,8 @@ fxt1_quantize_MIXED0 (uint32_t *cc,
 #else
    int32_t minVal;
    int32_t maxVal;
-   int32_t maxVarL = fxt1_variance(NULL, input, n_comp, N_TEXELS / 2);
-   int32_t maxVarR = fxt1_variance(NULL, &input[N_TEXELS / 2], n_comp, N_TEXELS / 2);
+   int32_t maxVarL = fxt1_variance(input, n_comp);
+   int32_t maxVarR = fxt1_variance(&input[N_TEXELS / 2], n_comp);
 
    /* Scan the channel with max variance for lo & hi
     * and use those as the two representative colors.