diff --git a/target/riscv/insn32-64.decode b/target/riscv/insn32-64.decode
index 8157dee8b7c..f4c42720fc7 100644
--- a/target/riscv/insn32-64.decode
+++ b/target/riscv/insn32-64.decode
@@ -86,3 +86,7 @@ fmv_d_x    1111001  00000 ..... 000 ..... 1010011 @r2
 hlv_wu    0110100  00001   ..... 100 ..... 1110011 @r2
 hlv_d     0110110  00000   ..... 100 ..... 1110011 @r2
 hsv_d     0110111  .....   ..... 100 00000 1110011 @r2_s
+
+# *** RV64B Standard Extension (in addition to RV32B) ***
+clzw       0110000 00000 ..... 001 ..... 0011011 @r2
+ctzw       0110000 00001 ..... 001 ..... 0011011 @r2
diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 3823b3ea800..8fe838cf0d0 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -40,6 +40,7 @@
 &i    imm rs1 rd
 &j    imm rd
 &r    rd rs1 rs2
+&r2   rd rs1
 &s    imm rs1 rs2
 &u    imm rd
 &shift     shamt rs1 rd
@@ -67,7 +68,7 @@
 @r4_rm   ..... ..  ..... ..... ... ..... ....... %rs3 %rs2 %rs1 %rm %rd
 @r_rm    .......   ..... ..... ... ..... ....... %rs2 %rs1 %rm %rd
 @r2_rm   .......   ..... ..... ... ..... ....... %rs1 %rm %rd
-@r2      .......   ..... ..... ... ..... ....... %rs1 %rd
+@r2      .......   ..... ..... ... ..... ....... &r2 %rs1 %rd
 @r2_nfvm ... ... vm:1 ..... ..... ... ..... ....... &r2nfvm %nf %rs1 %rd
 @r2_vm   ...... vm:1 ..... ..... ... ..... ....... &rmr %rs2 %rd
 @r1_vm   ...... vm:1 ..... ..... ... ..... ....... %rd
@@ -592,3 +593,7 @@ vcompress_vm    010111 - ..... ..... 010 ..... 1010111 @r
 
 vsetvli         0 ........... ..... 111 ..... 1010111  @r2_zimm
 vsetvl          1000000 ..... ..... 111 ..... 1010111  @r
+
+# *** RV32B Standard Extension ***
+clz        011000 000000 ..... 001 ..... 0010011 @r2
+ctz        011000 000001 ..... 001 ..... 0010011 @r2
diff --git a/target/riscv/insn_trans/trans_rvb.c.inc b/target/riscv/insn_trans/trans_rvb.c.inc
new file mode 100644
index 00000000000..76788c2f353
--- /dev/null
+++ b/target/riscv/insn_trans/trans_rvb.c.inc
@@ -0,0 +1,47 @@
+/*
+ * RISC-V translation routines for the RVB Standard Extension.
+ *
+ * Copyright (c) 2020 Kito Cheng, kito.cheng@sifive.com
+ * Copyright (c) 2020 Frank Chang, frank.chang@sifive.com
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+static bool trans_clz(DisasContext *ctx, arg_clz *a)
+{
+    REQUIRE_EXT(ctx, RVB);
+    return gen_unary(ctx, a, gen_clz);
+}
+
+static bool trans_ctz(DisasContext *ctx, arg_ctz *a)
+{
+    REQUIRE_EXT(ctx, RVB);
+    return gen_unary(ctx, a, gen_ctz);
+}
+
+/* RV64-only instructions */
+#ifdef TARGET_RISCV64
+
+static bool trans_clzw(DisasContext *ctx, arg_clzw *a)
+{
+    REQUIRE_EXT(ctx, RVB);
+    return gen_unary(ctx, a, gen_clzw);
+}
+
+static bool trans_ctzw(DisasContext *ctx, arg_ctzw *a)
+{
+    REQUIRE_EXT(ctx, RVB);
+    return gen_unary(ctx, a, gen_ctzw);
+}
+
+#endif
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index 2f9f5ccc621..4648c422f42 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -536,6 +536,23 @@ static bool gen_arith_div_uw(DisasContext *ctx, arg_r *a,
 
 #endif
 
+#ifdef TARGET_RISCV64
+
+static void gen_ctzw(TCGv ret, TCGv arg1)
+{
+    tcg_gen_ori_i64(ret, arg1, MAKE_64BIT_MASK(32, 32));
+    tcg_gen_ctzi_i64(ret, ret, 64);
+}
+
+static void gen_clzw(TCGv ret, TCGv arg1)
+{
+    tcg_gen_ext32u_i64(ret, arg1);
+    tcg_gen_clzi_i64(ret, ret, 64);
+    tcg_gen_subi_i64(ret, ret, 32);
+}
+
+#endif
+
 static bool gen_arith(DisasContext *ctx, arg_r *a,
                       void(*func)(TCGv, TCGv, TCGv))
 {
@@ -581,6 +598,30 @@ static uint32_t opcode_at(DisasContextBase *dcbase, target_ulong pc)
     return cpu_ldl_code(env, pc);
 }
 
+static void gen_ctz(TCGv ret, TCGv arg1)
+{
+    tcg_gen_ctzi_tl(ret, arg1, TARGET_LONG_BITS);
+}
+
+static void gen_clz(TCGv ret, TCGv arg1)
+{
+    tcg_gen_clzi_tl(ret, arg1, TARGET_LONG_BITS);
+}
+
+static bool gen_unary(DisasContext *ctx, arg_r2 *a,
+                      void(*func)(TCGv, TCGv))
+{
+    TCGv source = tcg_temp_new();
+
+    gen_get_gpr(source, a->rs1);
+
+    (*func)(source, source);
+
+    gen_set_gpr(a->rd, source);
+    tcg_temp_free(source);
+    return true;
+}
+
 /* Include insn module translation function */
 #include "insn_trans/trans_rvi.c.inc"
 #include "insn_trans/trans_rvm.c.inc"
@@ -589,6 +630,7 @@ static uint32_t opcode_at(DisasContextBase *dcbase, target_ulong pc)
 #include "insn_trans/trans_rvd.c.inc"
 #include "insn_trans/trans_rvh.c.inc"
 #include "insn_trans/trans_rvv.c.inc"
+#include "insn_trans/trans_rvb.c.inc"
 #include "insn_trans/trans_privileged.c.inc"
 
 /* Include the auto-generated decoder for 16 bit insn */
