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| author | Philippe Mathieu-Daudé <philmd@linaro.org> | 2023-08-23 16:55:36 +0200 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2023-08-24 11:22:42 -0700 |
| commit | 8b078800ab23c38e07a11dffbd88a988a6633152 (patch) | |
| tree | 7301a15ea2ba90ac31400d8bbc38d3f99ea66608 /tcg/tcg-op.c | |
| parent | 4de5a76a923e1afab28bfbf9d19b67368bf98fb8 (diff) | |
| download | focaccia-qemu-8b078800ab23c38e07a11dffbd88a988a6633152.tar.gz focaccia-qemu-8b078800ab23c38e07a11dffbd88a988a6633152.zip | |
tcg/tcg-op: Document bswap16_i64() byte pattern
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org> Message-Id: <20230823145542.79633-3-philmd@linaro.org> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Diffstat (limited to 'tcg/tcg-op.c')
| -rw-r--r-- | tcg/tcg-op.c | 27 |
1 files changed, 19 insertions, 8 deletions
diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c index fc3a0ab7fc..88c7c60ffe 100644 --- a/tcg/tcg-op.c +++ b/tcg/tcg-op.c @@ -1767,6 +1767,14 @@ void tcg_gen_ext32u_i64(TCGv_i64 ret, TCGv_i64 arg) } } +/* + * bswap16_i64: 16-bit byte swap on the low bits of a 64-bit value. + * + * Byte pattern: xxxxxxxxab -> yyyyyyyyba + * + * With TCG_BSWAP_IZ, x == zero, else undefined. + * With TCG_BSWAP_OZ, y == zero, with TCG_BSWAP_OS y == sign, else undefined. + */ void tcg_gen_bswap16_i64(TCGv_i64 ret, TCGv_i64 arg, int flags) { /* Only one extension flag may be present. */ @@ -1785,22 +1793,25 @@ void tcg_gen_bswap16_i64(TCGv_i64 ret, TCGv_i64 arg, int flags) TCGv_i64 t0 = tcg_temp_ebb_new_i64(); TCGv_i64 t1 = tcg_temp_ebb_new_i64(); - tcg_gen_shri_i64(t0, arg, 8); + /* arg = ......ab or xxxxxxab */ + tcg_gen_shri_i64(t0, arg, 8); /* t0 = .......a or .xxxxxxa */ if (!(flags & TCG_BSWAP_IZ)) { - tcg_gen_ext8u_i64(t0, t0); + tcg_gen_ext8u_i64(t0, t0); /* t0 = .......a */ } if (flags & TCG_BSWAP_OS) { - tcg_gen_shli_i64(t1, arg, 56); - tcg_gen_sari_i64(t1, t1, 48); + tcg_gen_shli_i64(t1, arg, 56); /* t1 = b....... */ + tcg_gen_sari_i64(t1, t1, 48); /* t1 = ssssssb. */ } else if (flags & TCG_BSWAP_OZ) { - tcg_gen_ext8u_i64(t1, arg); - tcg_gen_shli_i64(t1, t1, 8); + tcg_gen_ext8u_i64(t1, arg); /* t1 = .......b */ + tcg_gen_shli_i64(t1, t1, 8); /* t1 = ......b. */ } else { - tcg_gen_shli_i64(t1, arg, 8); + tcg_gen_shli_i64(t1, arg, 8); /* t1 = xxxxxab. */ } - tcg_gen_or_i64(ret, t0, t1); + tcg_gen_or_i64(ret, t0, t1); /* ret = ......ba (OZ) */ + /* ssssssba (OS) */ + /* xxxxxaba (no flag) */ tcg_temp_free_i64(t0); tcg_temp_free_i64(t1); } |