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const correctness msac

--- a/src/msac.c

+++ b/src/msac.c

@@ -38,7 +38,7 @@

 #define EC_WIN_SIZE (sizeof(ec_win) << 3)

-static inline void ctx_refill(MsacContext *s) {

+static inline void ctx_refill(MsacContext *const s) {

     const uint8_t *buf_pos = s->buf_pos;

     const uint8_t *buf_end = s->buf_end;

     int c = EC_WIN_SIZE - s->cnt - 24;

@@ -57,7 +57,9 @@

  * necessary), and stores them back in the decoder context.

  * dif: The new value of dif.

  * rng: The new value of the range. */

-static inline void ctx_norm(MsacContext *s, ec_win dif, unsigned rng) {

+static inline void ctx_norm(MsacContext *const s, const ec_win dif,

+                            const unsigned rng)

+{

     const int d = 15 ^ (31 ^ clz(rng));

     assert(rng <= 65535U);

     s->cnt -= d;

@@ -68,16 +70,16 @@

 }

 unsigned dav1d_msac_decode_bool_equi_c(MsacContext *const s) {

-    ec_win vw, dif = s->dif;

-    unsigned ret, v, r = s->rng;

+    const unsigned r = s->rng;

+    ec_win dif = s->dif;

     assert((dif >> (EC_WIN_SIZE - 16)) < r);

     // When the probability is 1/2, f = 16384 >> EC_PROB_SHIFT = 256 and we can

     // replace the multiply with a simple shift.

-    v = ((r >> 8) << 7) + EC_MIN_PROB;

-    vw   = (ec_win)v << (EC_WIN_SIZE - 16);

-    ret  = dif >= vw;

-    dif -= ret*vw;

-    v   += ret*(r - 2*v);

+    unsigned v = ((r >> 8) << 7) + EC_MIN_PROB;

+    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);

+    const unsigned ret = dif >= vw;

+    dif -= ret * vw;

+    v += ret * (r - 2 * v);

     ctx_norm(s, dif, v);

     return !ret;

 }

@@ -86,14 +88,14 @@

  * f: The probability that the bit is one

  * Return: The value decoded (0 or 1). */

 unsigned dav1d_msac_decode_bool_c(MsacContext *const s, const unsigned f) {

-    ec_win vw, dif = s->dif;

-    unsigned ret, v, r = s->rng;

+    const unsigned r = s->rng;

+    ec_win dif = s->dif;

     assert((dif >> (EC_WIN_SIZE - 16)) < r);

-    v = ((r >> 8) * (f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + EC_MIN_PROB;

-    vw   = (ec_win)v << (EC_WIN_SIZE - 16);

-    ret  = dif >= vw;

-    dif -= ret*vw;

-    v   += ret*(r - 2*v);

+    unsigned v = ((r >> 8) * (f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + EC_MIN_PROB;

+    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);

+    const unsigned ret = dif >= vw;

+    dif -= ret * vw;

+    v += ret * (r - 2 * v);

     ctx_norm(s, dif, v);

     return !ret;

 }