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From: Alistair Francis <alistair.francis@opensource.wdc.com>
To: qemu-devel@nongnu.org
Cc: alistair23@gmail.com, Philipp Tomsich <philipp.tomsich@vrull.eu>,
	Vincent Palatin <vpalatin@rivosinc.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	Alistair Francis <alistair.francis@wdc.com>
Subject: [PULL 03/33] target/riscv: Fix orc.b implementation
Date: Fri, 22 Oct 2021 23:37:42 +1000	[thread overview]
Message-ID: <20211022133812.3972903-4-alistair.francis@opensource.wdc.com> (raw)
In-Reply-To: <20211022133812.3972903-1-alistair.francis@opensource.wdc.com>

From: Philipp Tomsich <philipp.tomsich@vrull.eu>

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 <philipp.tomsich@vrull.eu>
Reported-by: Vincent Palatin <vpalatin@rivosinc.com>
Tested-by: Vincent Palatin <vpalatin@rivosinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211013184125.2010897-1-philipp.tomsich@vrull.eu
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 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);
-- 
2.31.1



  parent reply	other threads:[~2021-10-22 13:41 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-22 13:37 [PULL 00/33] riscv-to-apply queue Alistair Francis
2021-10-22 13:37 ` [PULL 01/33] target/riscv: Pass the same value to oprsz and maxsz for vmv.v.v Alistair Francis
2021-10-22 13:37 ` [PULL 02/33] target/riscv: line up all of the registers in the info register dump Alistair Francis
2021-10-22 13:37 ` Alistair Francis [this message]
2021-10-22 13:37 ` [PULL 04/33] hw/riscv: virt: Use machine->ram as the system memory Alistair Francis
2021-10-22 13:37 ` [PULL 05/33] target/riscv: fix TB_FLAGS bits overlapping bug for rvv/rvh Alistair Francis
2021-10-22 13:37 ` [PULL 06/33] target/riscv: Remove some unused macros Alistair Francis
2021-10-22 13:37 ` [PULL 07/33] target/riscv: Organise the CPU properties Alistair Francis
2021-10-22 13:37 ` [PULL 08/33] target/riscv: Move cpu_get_tb_cpu_state out of line Alistair Francis
2021-10-22 13:37 ` [PULL 09/33] target/riscv: Create RISCVMXL enumeration Alistair Francis
2021-10-22 13:37 ` [PULL 10/33] target/riscv: Split misa.mxl and misa.ext Alistair Francis
2021-10-22 13:37 ` [PULL 11/33] target/riscv: Replace riscv_cpu_is_32bit with riscv_cpu_mxl Alistair Francis
2021-10-22 13:37 ` [PULL 12/33] target/riscv: Add MXL/SXL/UXL to TB_FLAGS Alistair Francis
2021-10-22 13:37 ` [PULL 13/33] target/riscv: Use REQUIRE_64BIT in amo_check64 Alistair Francis
2021-10-22 13:37 ` [PULL 14/33] target/riscv: Properly check SEW in amo_op Alistair Francis
2021-10-22 13:37 ` [PULL 15/33] target/riscv: Replace is_32bit with get_xl/get_xlen Alistair Francis
2021-10-22 13:37 ` [PULL 16/33] target/riscv: Replace DisasContext.w with DisasContext.ol Alistair Francis
2021-10-22 13:37 ` [PULL 17/33] target/riscv: Use gen_arith_per_ol for RVM Alistair Francis
2021-10-22 13:37 ` [PULL 18/33] target/riscv: Adjust trans_rev8_32 for riscv64 Alistair Francis
2021-10-22 13:37 ` [PULL 19/33] target/riscv: Use gen_unary_per_ol for RVB Alistair Francis
2021-10-22 13:37 ` [PULL 20/33] target/riscv: Use gen_shift*_per_ol for RVB, RVI Alistair Francis
2021-10-22 13:38 ` [PULL 21/33] target/riscv: Use riscv_csrrw_debug for cpu_dump Alistair Francis
2021-10-22 13:38 ` [PULL 22/33] target/riscv: Compute mstatus.sd on demand Alistair Francis
2021-10-22 13:38 ` [PULL 23/33] hw/riscv: opentitan: Update to the latest build Alistair Francis
2021-10-22 13:38 ` [PULL 24/33] hw/intc: Remove the Ibex PLIC Alistair Francis
2021-10-22 13:38 ` [PULL 25/33] hw/intc: sifive_plic: Move the properties Alistair Francis
2021-10-22 13:38 ` [PULL 26/33] hw/intc: sifive_plic: Cleanup the realize function Alistair Francis
2021-10-22 13:38 ` [PULL 27/33] hw/intc: sifive_plic: Cleanup the irq_request function Alistair Francis
2021-10-22 13:38 ` [PULL 28/33] hw/riscv: microchip_pfsoc: Use MachineState::ram and MachineClass::default_ram_id Alistair Francis
2021-10-22 13:38 ` [PULL 29/33] hw/riscv: opentitan: " Alistair Francis
2021-10-22 13:38 ` [PULL 30/33] hw/riscv: shakti_c: " Alistair Francis
2021-10-22 13:38 ` [PULL 31/33] hw/riscv: sifive_e: " Alistair Francis
2021-10-22 13:38 ` [PULL 32/33] hw/riscv: sifive_u: " Alistair Francis
2021-10-22 13:38 ` [PULL 33/33] hw/riscv: spike: " Alistair Francis
2021-10-22 21:39 ` [PULL 00/33] riscv-to-apply queue Richard Henderson

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