A.5.116 IBTS: Insert Bit String
IBTS r/m16,reg16 ; o16 0F A7 /r [386,UNDOC]
IBTS r/m32,reg32 ; o32 0F A7 /r [386,UNDOC]
The implied operation of this instruction is:
IBTS r/m16,AX,CL,reg16
IBTS r/m32,EAX,CL,reg32
Writes a bit string from the source operand to the destination. CL
indicates the number of bits to be copied, from the low bits of the
source. (E)AX indicates the low order bit offset in the destination that
is written to. For example, if CL is set to 4 and AX (for 16-bit code)
is set to 5, bits 0-3 of "src" will be copied to bits 5-8 of "dst". This
instruction is very poorly documented, and I have been unable to find
any official source of documentation on it.
IBTS is supported only on the early Intel 386s, and conflicts with the
opcodes for CMPXCHG486 (on early Intel 486s). NASM supports it only for
completeness. Its counterpart is XBTS (see section A.5.332).