On 7 January 2011 22:42, Richard Henderson <r...@twiddle.net> wrote: > Emulating i386 -- particularly in 16-bit mode -- requires quite a few > bitfield insert operations, to handle byte and word stores into the > dword registers. On several hosts, this can be done natively, without > resorting to a sequence of and and or instructions.
+* deposit_i32/i64 dest, t1, t2, loc + +Deposit T2 as a bitfield into T1, placing the result in DEST. +The bitfield is described by LOC, an immediate value: + + bits 0:7 - the length of the bitfield + bits 8:15 - the position of the first bit + +For example, 0x101 indicates a 1-bit field at bit 1. +This operation would be equivalent to + + dest = (t1 & ~2) | ((t2 << 1) & 2) Unless I've missed something, deposit_i32 is basically the same as the ARM BFI instruction, so for ARM we could use deposit_i32 in the implementation of BFI (and conversely implement deposit_i32 using BFI when we're generating for an ARMv6T2 or better host.) -- PMM
