On 22/8/23 15:42, Alex Bennée wrote:
Philippe Mathieu-Daudé <phi...@linaro.org> writes:
While reviewing a recent patch from Richard optimizing
deposit() [*] I ended looking at the *swap friends, taking
some notes, which then evolved to proper documentation.
[*]
https://lore.kernel.org/qemu-devel/20230816145547.477974-3-richard.hender...@linaro.org/
We already have some documentation in tcg.rst:
* - bswap16_i32/i64 *t0*, *t1*, *flags*
- | 16 bit byte swap on the low bits of a 32/64 bit input.
|
| If *flags* & ``TCG_BSWAP_IZ``, then *t1* is known to be zero-extended
from bit 15.
| If *flags* & ``TCG_BSWAP_OZ``, then *t0* will be zero-extended from
bit 15.
| If *flags* & ``TCG_BSWAP_OS``, then *t0* will be sign-extended from
bit 15.
|
| If neither ``TCG_BSWAP_OZ`` nor ``TCG_BSWAP_OS`` are set, then the
bits of *t0* above bit 15 may contain any value.
* - bswap32_i64 *t0*, *t1*, *flags*
- | 32 bit byte swap on a 64-bit value. The flags are the same as for
bswap16,
except they apply from bit 31 instead of bit 15.
* - bswap32_i32 *t0*, *t1*, *flags*
bswap64_i64 *t0*, *t1*, *flags*
- | 32/64 bit byte swap. The flags are ignored, but still present
for consistency with the other bswap opcodes.
I guess I wasn't clear enough: I mostly documented the implementation,
not the API.
That said, maybe the bytes movement pattern belong to the API doc
(at least I find it very useful to find which TCG opcode implement
the frontend code, when the TCG opcode name isn't trivial, although
documented).
