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Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/extend.texi | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 0b572af..4b77599 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -16974,6 +16974,23 @@ __builtin_avr_insert_bits (0x01234567, bits, 0); @end smallexample @enddefbuiltin +@defbuiltin{uint8_t __builtin_avr_mask1 (uint8_t @var{mask}, uint8_t @var{offs})} +Rotate the 8-bit constant value @var{mask} by an offset of @var{offs}, +where @var{mask} is in @{ 0x01, 0xfe, 0x7f, 0x80 @}. +This built-in can be use as an alternative to 8-bit expressions like +@code{1 << offs} when their computation consumes too much +time, and @var{offs} is known to be in the range 0@dots{}7. +@example +__builtin_avr_mask1 (1, offs) // same like 1 << offs +__builtin_avr_mask1 (~1, offs) // same like ~(1 << offs) +__builtin_avr_mask1 (0x80, offs) // same like 0x80 >> offs +__builtin_avr_mask1 (~0x80, offs) // same like ~(0x80 >> offs) +@end example +The open coded C versions take at least @code{5 + 4 * @var{offs}} cycles +(and 5 instructions), whereas the built-in takes 7 cycles and instructions +(8 cycles and instructions in the case of @code{@var{mask} = 0x7f}). +@enddefbuiltin + @defbuiltin{void __builtin_avr_nops (uint16_t @var{count})} Insert @var{count} @code{NOP} instructions. The number of instructions must be a compile-time integer constant. |