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([2602:47:d483:7301:4e3c:f4a4:b92a:b5ab]) by smtp.gmail.com with ESMTPSA id u1-20020a170902e80100b001b51b3e84cesm9196589plg.166.2023.08.22.08.58.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Aug 2023 08:58:08 -0700 (PDT) Message-ID: Date: Tue, 22 Aug 2023 08:58:06 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 1/7] tcg/tcg-op: Document bswap16() byte pattern Content-Language: en-US To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org Cc: "Edgar E. Iglesias" , Paolo Bonzini References: <20230822093712.38922-1-philmd@linaro.org> <20230822093712.38922-2-philmd@linaro.org> From: Richard Henderson In-Reply-To: <20230822093712.38922-2-philmd@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::629; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x629.google.com X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.767, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 8/22/23 02:37, Philippe Mathieu-Daudé wrote: > Signed-off-by: Philippe Mathieu-Daudé > --- > tcg/tcg-op.c | 48 ++++++++++++++++++++++++++++++++---------------- > 1 file changed, 32 insertions(+), 16 deletions(-) > > diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c > index 7aadb37756..f164ddc95e 100644 > --- a/tcg/tcg-op.c > +++ b/tcg/tcg-op.c > @@ -1021,6 +1021,13 @@ void tcg_gen_ext16u_i32(TCGv_i32 ret, TCGv_i32 arg) > } > } > > +/* > + * bswap16_i32: 16-bit byte swap on the low bits of a 32-bit value. > + * > + * Byte pattern: bswap16_i32(xxab) -> ..ba (TCG_BSWAP_OZ) > + * bswap16_i32(xxab) -> ssba (TCG_BSWAP_OS) > + * bswap16_i32(xxab) -> xxba > + */ Don't forget TCG_BSWAP_IZ, which means the input is already zero-extended. Which makes > + /* arg = xxab */ > + tcg_gen_shri_i32(t0, arg, 8); /* t0 = .xxa */ this > if (!(flags & TCG_BSWAP_IZ)) { > - tcg_gen_ext8u_i32(t0, t0); > + tcg_gen_ext8u_i32(t0, t0); /* t0 = ...a */ > } > > if (flags & TCG_BSWAP_OS) { > - tcg_gen_shli_i32(t1, arg, 24); > - tcg_gen_sari_i32(t1, t1, 16); > + tcg_gen_shli_i32(t1, arg, 24); /* t1 = b... */ > + tcg_gen_sari_i32(t1, t1, 16); /* t1 = ssb. */ > } else if (flags & TCG_BSWAP_OZ) { > - tcg_gen_ext8u_i32(t1, arg); > - tcg_gen_shli_i32(t1, t1, 8); > + tcg_gen_ext8u_i32(t1, arg); /* t1 = ...b */ > + tcg_gen_shli_i32(t1, t1, 8); /* t1 = ..b. */ > } else { > - tcg_gen_shli_i32(t1, arg, 8); > + tcg_gen_shli_i32(t1, arg, 8); /* t1 = xab. */ and this slightly inaccurate. > } > > - tcg_gen_or_i32(ret, t0, t1); > + tcg_gen_or_i32(ret, t0, t1); /* ret = ssba */ This one is just confusing, since each of the three cases above have different outputs. r~ r~