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ibts

Insert bit string Undocumented

Inserts a bit string from the source operand into the destination.

386 and laterremoved from the architectureNot available in 64-bit mode

Forms

Operands

r/m
A general-purpose register or memory location matching the operation’s size, for example rax or qword [rbp-8]. The byte registers ah, bh, ch and dh cannot be used with a REX prefix, including when the memory address uses r8–r15.
reg
A general-purpose register matching the operation’s size, for example al, ax, eax or rax. The byte registers ah, bh, ch and dh cannot be used with a REX prefix, which is required by spl, bpl, sil, dil and r8–r15.

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.