mlkem: gen_matrix.jinc update from formosa-crypto/formosa-mlkem#19

Author: tfaoliveira

src/crypto_kem/mlkem/mlkem768/amd64/avx2/gen_matrix.jinc

@@ -9,54 +9,46 @@ fn __rej_uniform(stack u16[MLKEM_N] rp, reg u64 offset, stack u8[SHAKE128_RATE]
   reg u16 val1 val2;
   reg u16 t;
   reg u64 pos ctr;
-  reg u64 cnd0 cnd1 exit;
 
 
   ctr = offset;
   pos = 0;
-  exit = 0;
 
-  while(exit == 0)
-  {
-    val1 = (16u)buf[(int)pos];
-    pos += 1;
-    t   = (16u)buf[(int)pos];
-    val2 = t;
-    val2 >>= 4;
-    t &= 0x0F;
-    t <<= 8;
-    val1 |= t;
-    pos += 1;
-
-    t   = (16u)buf[(int)pos];
-    t <<= 4;
-    val2 |= t;
-    pos += 1;
-
-    if(val1 < MLKEM_Q)
-    {
-      rp[(int)ctr] = val1;
-      ctr += 1;
-    }
-
-    if(val2 < MLKEM_Q)
-    {
-      if(ctr < MLKEM_N)
-      {
-        rp[(int)ctr] = val2;
+  while (pos < SHAKE128_RATE - 2) {
+    if ctr < MLKEM_N {
+      val1 = (16u)buf[pos];
+      t   = (16u)buf[pos + 1];
+      val2 = t;
+      val2 >>= 4;
+      t &= 0x0F;
+      t <<= 8;
+      val1 |= t;
+
+      t   = (16u)buf[pos + 2];
+      t <<= 4;
+      val2 |= t;
+      pos += 3;
+
+      reg bool cond;
+      #[declassify]
+      cond = val1 < MLKEM_Q;
+      if cond {
+        rp[ctr] = val1;
         ctr += 1;
       }
-    }
 
-    // Check if we should exit the loop
-    cnd0  = MLKEM_N;
-    cnd0 -= ctr;
-    cnd0 -= 1;
-    cnd1  = SHAKE128_RATE;
-    cnd1 -= pos;
-    cnd1 -= 3; //TODO: (potentially) wasting 2 'good' bytes
-    exit  = cnd0 | cnd1;
-    exit >>= 63;
+      #[declassify]
+      cond = val2 < MLKEM_Q;
+      if cond {
+        if(ctr < MLKEM_N)
+        {
+          rp[ctr] = val2;
+          ctr += 1;
+        }
+      }
+    } else {
+      pos = SHAKE128_RATE;
+    }
   }
 
   return ctr, rp;

src/crypto_kem/mlkem/mlkem768/amd64/ref/gen_matrix.jinc

@@ -7,54 +7,46 @@ fn __rej_uniform(stack u16[MLKEM_N] rp, reg u64 offset, stack u8[SHAKE128_RATE]
   reg u16 val1 val2;
   reg u16 t;
   reg u64 pos ctr;
-  reg u64 cnd0 cnd1 exit;
 
 
   ctr = offset;
   pos = 0;
-  exit = 0;
 
-  while(exit == 0)
-  {
-    val1 = (16u)buf[(int)pos];
-    pos += 1;
-    t   = (16u)buf[(int)pos];
-    val2 = t;
-    val2 >>= 4;
-    t &= 0x0F;
-    t <<= 8;
-    val1 |= t;
-    pos += 1;
-
-    t   = (16u)buf[(int)pos];
-    t <<= 4;
-    val2 |= t;
-    pos += 1;
-
-    if(val1 < MLKEM_Q)
-    {
-      rp[(int)ctr] = val1;
-      ctr += 1;
-    }
-
-    if(val2 < MLKEM_Q)
-    {
-      if(ctr < MLKEM_N)
-      {
-        rp[(int)ctr] = val2;
+  while (pos < SHAKE128_RATE - 2) {
+    if ctr < MLKEM_N {
+      val1 = (16u)buf[pos];
+      t   = (16u)buf[pos + 1];
+      val2 = t;
+      val2 >>= 4;
+      t &= 0x0F;
+      t <<= 8;
+      val1 |= t;
+
+      t   = (16u)buf[pos + 2];
+      t <<= 4;
+      val2 |= t;
+      pos += 3;
+
+      reg bool cond;
+      #[declassify]
+      cond = val1 < MLKEM_Q;
+      if cond {
+        rp[ctr] = val1;
         ctr += 1;
       }
-    }
 
-    // Check if we should exit the loop
-    cnd0  = MLKEM_N;
-    cnd0 -= ctr;
-    cnd0 -= 1;
-    cnd1  = SHAKE128_RATE;
-    cnd1 -= pos;
-    cnd1 -= 3; //TODO: (potentially) wasting 2 'good' bytes
-    exit  = cnd0 | cnd1;
-    exit >>= 63;
+      #[declassify]
+      cond = val2 < MLKEM_Q;
+      if cond {
+        if(ctr < MLKEM_N)
+        {
+          rp[ctr] = val2;
+          ctr += 1;
+        }
+      }
+    } else {
+      pos = SHAKE128_RATE;
+    }
   }
 
   return ctr, rp;