Add De Bruijn helper for O(1) priority lookup

This commit introduces a 32-entry De Bruijn lookup table to support
constant-time bitmap index computation. This mechanism will be used in
later commits to replace iterative bit-scanning when selecting the next
runnable priority.

The helper itself does not change any scheduling behavior yet, but lays
the groundwork for the new O(1) scheduler’s priority computation path.

Author: vicLin8712

kernel/task.c

@@ -356,6 +356,23 @@ void panic(int32_t ecode)
     hal_panic();
 }
 
+/* RISC-V optimized priority finding using De Bruijn sequence */
+static const uint8_t debruijn_lut[32] = {
+    0,  1,  28, 2,  29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4,  8,
+    31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6,  11, 5,  10, 9};
+
+/* O(1) priority selection optimized for RISC-V */
+static inline uint8_t find_highest_ready_priority(uint32_t bitmap)
+{
+    /* Isolate rightmost set bit (highest priority) */
+    uint32_t isolated = bitmap & (-bitmap);
+
+    /* De Bruijn multiplication for O(1) bit position finding */
+    uint32_t hash = (isolated * 0x077CB531U) >> 27;
+
+    return debruijn_lut[hash & 0x1F];
+}
+
 /* Weak aliases for context switching functions. */
 void dispatch(void);
 void yield(void);