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Sib->scale

Access the |X86ISA|::|SCALE| field of a sib bit structure.

Signature
(sib->scale x) → scale
Arguments: x — Guard (sib-p x).
Returns: scale — Type (2bits-p scale).

Definitions and Theorems

Function: sib->scale$inline

(defun sib->scale$inline (x)
 (declare (xargs :guard (sib-p x)))
 (mbe
     :logic
     (let ((x (sib-fix x)))
       (part-select x :low 6 :width 2))
     :exec (the (unsigned-byte 2)
                (logand (the (unsigned-byte 2) 3)
                        (the (unsigned-byte 2)
                             (ash (the (unsigned-byte 8) x) -6))))))

Theorem: 2bits-p-of-sib->scale

(defthm 2bits-p-of-sib->scale
  (b* ((scale (sib->scale$inline x)))
    (2bits-p scale))
  :rule-classes :rewrite)

Theorem: sib->scale$inline-of-sib-fix-x

(defthm sib->scale$inline-of-sib-fix-x
  (equal (sib->scale$inline (sib-fix x))
         (sib->scale$inline x)))

Theorem: sib->scale$inline-sib-equiv-congruence-on-x

(defthm sib->scale$inline-sib-equiv-congruence-on-x
  (implies (sib-equiv x x-equiv)
           (equal (sib->scale$inline x)
                  (sib->scale$inline x-equiv)))
  :rule-classes :congruence)

Theorem: sib->scale-of-sib

(defthm sib->scale-of-sib
  (equal (sib->scale (sib base index scale))
         (2bits-fix scale)))

Theorem: sib->scale-of-write-with-mask

(defthm sib->scale-of-write-with-mask
 (implies
   (and (fty::bitstruct-read-over-write-hyps x sib-equiv-under-mask)
        (sib-equiv-under-mask x y fty::mask)
        (equal (logand (lognot fty::mask) 192)
               0))
   (equal (sib->scale x) (sib->scale y))))