Updated poly_tomsg to prevent a compiler from using DIV. Thanks to Go…

…utam Tamvada, Karthikeyan Bhargavan, and Franziskus Kiefer @cryspen for pointing this out
pq-crystals · Dec 1, 2023 · dda29cc · dda29cc
1 parent a621b8d
commit dda29cc
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Showing 2 changed files with 9 additions and 3 deletions.
diff --git a/ref/poly.c b/ref/poly.c
@@ -180,14 +180,19 @@ void poly_frommsg(poly *r, const uint8_t msg[KYBER_INDCPA_MSGBYTES])
 void poly_tomsg(uint8_t msg[KYBER_INDCPA_MSGBYTES], const poly *a)
 {
   unsigned int i,j;
-  uint16_t t;
+  uint32_t t;
 
   for(i=0;i<KYBER_N/8;i++) {
     msg[i] = 0;
     for(j=0;j<8;j++) {
       t  = a->coeffs[8*i+j];
-      t += ((int16_t)t >> 15) & KYBER_Q;
-      t  = (((t << 1) + KYBER_Q/2)/KYBER_Q) & 1;
+      // t += ((int16_t)t >> 15) & KYBER_Q;
+      // t  = (((t << 1) + KYBER_Q/2)/KYBER_Q) & 1;
+      t <<= 1;
+      t += 1665;
+      t *= 80635;
+      t >>= 28;
+      t &= 1;
       msg[i] |= t << j;
     }
   }

diff --git a/runtests.sh b/runtests.sh
@@ -10,6 +10,7 @@ else
 fi
 
 if [ "$ARCH" = "amd64" -o "$ARCH" = "arm64" ]; then
+  export CC="clang"
   export CFLAGS="-fsanitize=address,undefined ${CFLAGS}"
 fi