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| author | Philippe Mathieu-Daudé <philmd@linaro.org> | 2023-08-23 16:55:35 +0200 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2023-08-24 11:22:42 -0700 |
| commit | 4de5a76a923e1afab28bfbf9d19b67368bf98fb8 (patch) | |
| tree | 1532361769fa238e01571af1c536f139e2e5df9e /tcg/tcg-op.c | |
| parent | 95bf306e3a058a38f5adb27be2ac598134b159d9 (diff) | |
| download | focaccia-qemu-4de5a76a923e1afab28bfbf9d19b67368bf98fb8.tar.gz focaccia-qemu-4de5a76a923e1afab28bfbf9d19b67368bf98fb8.zip | |
tcg/tcg-op: Document bswap16_i32() byte pattern
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org> Message-Id: <20230823145542.79633-2-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 b59a50a5a9..fc3a0ab7fc 100644 --- a/tcg/tcg-op.c +++ b/tcg/tcg-op.c @@ -1035,6 +1035,14 @@ 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: xxab -> yyba + * + * 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_i32(TCGv_i32 ret, TCGv_i32 arg, int flags) { /* Only one extension flag may be present. */ @@ -1046,22 +1054,25 @@ void tcg_gen_bswap16_i32(TCGv_i32 ret, TCGv_i32 arg, int flags) TCGv_i32 t0 = tcg_temp_ebb_new_i32(); TCGv_i32 t1 = tcg_temp_ebb_new_i32(); - tcg_gen_shri_i32(t0, arg, 8); + /* arg = ..ab (IZ) xxab (!IZ) */ + tcg_gen_shri_i32(t0, arg, 8); /* t0 = ...a (IZ) .xxa (!IZ) */ 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. */ } - tcg_gen_or_i32(ret, t0, t1); + tcg_gen_or_i32(ret, t0, t1); /* ret = ..ba (OZ) */ + /* = ssba (OS) */ + /* = xaba (no flag) */ tcg_temp_free_i32(t0); tcg_temp_free_i32(t1); } |