| -rw-r--r-- | doc/body.texi | 29 |
diff --git a/doc/body.texi b/doc/body.texi index 1c6d23e..f6d850e 100644 --- a/doc/body.texi +++ b/doc/body.texi @@ -375,6 +375,35 @@ movr _f _d O1 = O2 movi _f _d O1 = O2 extr _c _uc _s _us _i _ui _f _d O1 = O2 truncr _f _d O1 = trunc(O2) +ext O1 = sign_extend(O2[O3:O3+04]) +ext_u O1 = O2[O3:O3+04] +dep O1[O3:O3+O4] = O2 +@end example + +@code{ext}, @code{ext_u} and @code{dep} are useful to access @code{C} +compatible bit fields, provided that these are contained in a machine +word. @code{ext} is used to @emph{extract} and signed extend a value +from a bit field. @code{ext_u} is used to @{emph{extract} and zero +extend a value from a bit field. @code{dep} is used to @emph{deposit} +a value into a bit field. + +@example +ext(result, source, offset, length) +ext_u(result, source, offset, length) +dep(result, source, offset, length) +@end example + +The usual idiom to declare @code{C} and @lightning{} compatible bit fields is: +@example +union @{ + struct @{ + jit_word_t signed_bits: @code<length>; + jit_uword_t unsigned_bits: @code<length>; + ... + @} s; + jit_word_t signed_value; + jit_uword_t unsigned_value; +@} u; @end example In 64-bit architectures it may be required to use @code{truncr_f_i}, |