use zeromem() where appropriate

src/prngs/chacha20.c

@@ -71,7 +71,7 @@ int chacha20_prng_add_entropy(const unsigned char *in, unsigned long inlen, prng
       /* iv 8 bytes */
       if ((err = chacha_ivctr64(&prng->chacha.s, buf + 32, 8, 0)) != CRYPT_OK) goto LBL_UNLOCK;
       /* clear KEY + IV */
-      XMEMSET(buf, 0, sizeof(buf));
+      zeromem(buf, sizeof(buf));
    }
    else {
       /* chacha20_prng_ready() was not called yet, add entropy to ent buffer */

src/prngs/rc4.c

@@ -72,6 +72,7 @@ int rc4_add_entropy(const unsigned char *in, unsigned long inlen, prng_state *pr
       if ((err = rc4_stream_setup(&prng->rc4.s, buf, sizeof(buf))) != CRYPT_OK) goto LBL_UNLOCK;
       /* drop first 3072 bytes - https://en.wikipedia.org/wiki/RC4#Fluhrer.2C_Mantin_and_Shamir_attack */
       for (i = 0; i < 12; i++) rc4_stream_keystream(&prng->rc4.s, buf, sizeof(buf));
+      zeromem(buf, sizeof(buf));
    }
    else {
       /* rc4_ready() was not called yet, add entropy to the buffer */

src/prngs/sober128.c

@@ -73,7 +73,7 @@ int sober128_add_entropy(const unsigned char *in, unsigned long inlen, prng_stat
       /* iv 8 bytes */
       if ((err = sober128_stream_setiv(&prng->sober128.s, buf + 32, 8)) != CRYPT_OK) goto LBL_UNLOCK;
       /* clear KEY + IV */
-      XMEMSET(buf, 0, sizeof(buf));
+      zeromem(buf, sizeof(buf));
    }
    else {
       /* sober128_ready() was not called yet, add entropy to ent buffer */