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Split out the arm64 ID field comparison function

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This will be useful in an update for finding which HWCAPS to set.

Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31200
This commit is contained in:
Andrew Turner 2021-07-16 12:46:59 +00:00
parent b7a78d573a
commit 04f6015706
1 changed files with 32 additions and 16 deletions
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48
sys/arm64/arm64/identcpu.c
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@ -1147,22 +1147,26 @@ get_kernel_reg(u_int reg, uint64_t *val)
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 @@ update_lower_register(uint64_t val, uint64_t new_val, u_int shift,
* 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);