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Index: sys/arm64/arm64/identcpu.c
===================================================================
--- sys/arm64/arm64/identcpu.c
+++ sys/arm64/arm64/identcpu.c
@@ -1147,22 +1147,26 @@
return (false);
}
-static uint64_t
-update_lower_register(uint64_t val, uint64_t new_val, u_int shift,
- int width, bool sign)
+/*
+ * Compares two field values that may be signed or unsigned.
+ * Returns:
+ * < 0 when a is less than b
+ * = 0 when a equals b
+ * > 0 when a is greater than b
+ */
+static int
+mrs_field_cmp(uint64_t a, uint64_t b, u_int shift, int width, bool sign)
{
uint64_t mask;
- uint64_t new_field, old_field;
- bool update;
KASSERT(width > 0 && width < 64, ("%s: Invalid width %d", __func__,
width));
mask = (1ul << width) - 1;
- new_field = (new_val >> shift) & mask;
- old_field = (val >> shift) & mask;
+ /* Move the field to the lower bits */
+ a = (a >> shift) & mask;
+ b = (b >> shift) & mask;
- update = false;
if (sign) {
/*
* The field is signed. Toggle the upper bit so the comparison
@@ -1170,17 +1174,29 @@
* i.e. those with a 0 bit, larger than negative numbers,
* i.e. those with a 1 bit, in an unsigned comparison.
*/
- if ((new_field ^ (1ul << (width - 1))) <
- (old_field ^ (1ul << (width - 1))))
- update = true;
- } else {
- if (new_field < old_field)
- update = true;
+ a ^= 1ul << (width - 1);
+ b ^= 1ul << (width - 1);
}
- if (update) {
+ return (a - b);
+}
+
+static uint64_t
+update_lower_register(uint64_t val, uint64_t new_val, u_int shift,
+ int width, bool sign)
+{
+ uint64_t mask;
+
+ KASSERT(width > 0 && width < 64, ("%s: Invalid width %d", __func__,
+ width));
+
+ /*
+ * If the new value is less than the existing value update it.
+ */
+ if (mrs_field_cmp(new_val, val, shift, width, sign) < 0) {
+ mask = (1ul << width) - 1;
val &= ~(mask << shift);
- val |= new_field << shift;
+ val |= new_val & (mask << shift);
}
return (val);

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