From 54c17609372bb119575f3bb7309ea57fc1a58d1d Mon Sep 17 00:00:00 2001 From: Philipp Tomsich Date: Wed, 13 Oct 2021 20:41:25 +0200 Subject: target/riscv: Fix orc.b implementation The earlier implementation fell into a corner case for bytes that were 0x01, giving a wrong result (but not affecting our application test cases for strings, as an ASCII value 0x01 is rare in those...). This changes the algorithm to: 1. Mask out the high-bit of each bytes (so that each byte is <= 127). 2. Add 127 to each byte (i.e. if the low 7 bits are not 0, this will overflow into the highest bit of each byte). 3. Bitwise-or the original value back in (to cover those cases where the source byte was exactly 128) to saturate the high-bit. 4. Shift-and-mask (implemented as a mask-and-shift) to extract the MSB of each byte into its LSB. 5. Multiply with 0xff to fan out the LSB to all bits of each byte. Fixes: d7a4fcb034 ("target/riscv: Add orc.b instruction for Zbb, removing gorc/gorci") Signed-off-by: Philipp Tomsich Reported-by: Vincent Palatin Tested-by: Vincent Palatin Reviewed-by: Richard Henderson Message-id: 20211013184125.2010897-1-philipp.tomsich@vrull.eu Signed-off-by: Alistair Francis --- target/riscv/insn_trans/trans_rvb.c.inc | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/target/riscv/insn_trans/trans_rvb.c.inc b/target/riscv/insn_trans/trans_rvb.c.inc index 185c3e9a60..3095624f32 100644 --- a/target/riscv/insn_trans/trans_rvb.c.inc +++ b/target/riscv/insn_trans/trans_rvb.c.inc @@ -249,13 +249,16 @@ static bool trans_rev8_64(DisasContext *ctx, arg_rev8_64 *a) static void gen_orc_b(TCGv ret, TCGv source1) { TCGv tmp = tcg_temp_new(); - TCGv ones = tcg_constant_tl(dup_const_tl(MO_8, 0x01)); + TCGv low7 = tcg_constant_tl(dup_const_tl(MO_8, 0x7f)); - /* Set lsb in each byte if the byte was zero. */ - tcg_gen_sub_tl(tmp, source1, ones); - tcg_gen_andc_tl(tmp, tmp, source1); + /* Set msb in each byte if the byte was non-zero. */ + tcg_gen_and_tl(tmp, source1, low7); + tcg_gen_add_tl(tmp, tmp, low7); + tcg_gen_or_tl(tmp, tmp, source1); + + /* Extract the msb to the lsb in each byte */ + tcg_gen_andc_tl(tmp, tmp, low7); tcg_gen_shri_tl(tmp, tmp, 7); - tcg_gen_andc_tl(tmp, ones, tmp); /* Replicate the lsb of each byte across the byte. */ tcg_gen_muli_tl(ret, tmp, 0xff); -- cgit v1.2.3