diff --git a/is-my-code-constant-time?.md b/is-my-code-constant-time?.md
index 010b1b2..d114d8b 100644
--- a/is-my-code-constant-time?.md
+++ b/is-my-code-constant-time?.md
@@ -37,12 +37,12 @@ __INLINE void cpSM2KE_reduction_x2w(BNU_CHUNK_T *r, const BNU_CHUNK_T *a, const
    const int w = ((elemBits + 1) / 2 - 1);
 
    /* compute copy BNU_CHUNK */
-   const int num_copy_bc   = (w + (BNU_CHUNK_BITS - 1)) / BNU_CHUNK_BITS; // 2
+   const int num_copy_bc   = (w + (BNU_CHUNK_BITS - 1)) / BNU_CHUNK_BITS; // 2, 假定BNU_CHUNK_BITS=64
    const int num_bit_shift = (w - (num_copy_bc - 1) * BNU_CHUNK_BITS);  // 63
    const BNU_CHUNK_T vadd  = (BNU_CHUNK_T)(1ULL << num_bit_shift); // 1<<63 = 0x8000000000000000
    const BNU_CHUNK_T mask  = (BNU_CHUNK_T)(vadd - 1); // 0x7fffffffffffffff
 
-   ZEXPAND_COPY_BNU(r, elemSize, a, num_copy_bc);  // copy 2 64 bits of a to r
+   ZEXPAND_COPY_BNU(r, elemSize, a, num_copy_bc);  // copy 2 64 bits from a to r
    r[num_copy_bc - 1] = (r[num_copy_bc - 1] & mask) + vadd;
    return;
 }