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tcg/tcg-op: Document bswap16_i64() byte pattern

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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>
This commit is contained in:
Philippe Mathieu-Daudé 2023-08-23 16:55:36 +02:00 committed by Richard Henderson
parent 4de5a76a92
commit 8b078800ab
1 changed files with 19 additions and 8 deletions
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27
tcg/tcg-op.c
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@ -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);
}