On 8/22/23 02:37, Philippe Mathieu-Daudé wrote:
Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
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~
