WebP/Lossy: Tweak some comments

Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp

@@ -938,8 +938,7 @@ void predict_y_subblock(Span<i16> y_prediction, IntraBlockMode mode, int x, int
     auto at = [&y_prediction, y, x](int px, int py) -> i16& { return y_prediction[(4 * y + py) * 16 + 4 * x + px]; };
 
     if (mode == B_DC_PRED) {
-        // XXX spec text says this is like DC_PRED but predict_dc_nxn() in the sample impl looks like it doesn't do the "oob isn't read" part. what's right?
-        // DC16NoTopLeft_C vs DC4_C in libwebp dec.c / common_dec.h suggests the spec text is incomplete :/
+        // The spec text says this is like DC_PRED, but predict_dc_nxn() in the sample implementation doesn't do the "oob isn't read" part.
         int sum = 0, n = 8;
         for (int i = 0; i < 4; ++i)
             sum += left[i] + above[i];
@@ -952,12 +951,14 @@ void predict_y_subblock(Span<i16> y_prediction, IntraBlockMode mode, int x, int
             for (int px = 0; px < 4; ++px)
                 y_prediction[(4 * y + py) * 16 + 4 * x + px] = clamp(left[py] + above[px] - corner, 0, 255);
     } else if (mode == B_VE_PRED) {
+        // The spec text says this is like V_PRED, but the sample implementation shows it does weighted averages (unlike V_PRED).
         for (int py = 0; py < 4; ++py)
             for (int px = 0; px < 4; ++px) {
                 auto top_left = (px > 0 ? above[px - 1] : corner);
                 y_prediction[(4 * y + py) * 16 + 4 * x + px] = weighted_average(top_left, above[px], above[px + 1]);
             }
     } else if (mode == B_HE_PRED) {
+        // The spec text says this is like H_PRED, but the sample implementation shows it does weighted averages (unlike H_PRED).
         for (int py = 0; py < 4; ++py)
             for (int px = 0; px < 4; ++px) {
                 if (py == 0) {
@@ -1047,12 +1048,10 @@ void add_idct_to_prediction(Span<i16> prediction, Coefficients coefficients, int
     short_idct4x4llm_c(coefficients, idct_output, 4 * sizeof(i16));
 
     // https://datatracker.ietf.org/doc/html/rfc6386#section-14.5 "Summation of Predictor and Residue"
-    for (int py = 0; py < 4; ++py) { // Loop over 4x4 pixels in subblock
+    for (int py = 0; py < 4; ++py) {
         for (int px = 0; px < 4; ++px) {
-            // sum with prediction
             i16& p = prediction[(4 * y + py) * N + (4 * x + px)];
             p += idct_output[py * 4 + px];
-            // p = clamp(p, 0, 255);
         }
     }
 }