3-643
INSTRUCTION SET REFERENCE
SHRDDouble Precision Shift Right
Description
This instruction shifts the first operand (destination operand) to the right the number of bits spec-
ified by the third operand (count operand). The second operand (source operand) provides bits
to shift in from the left (starting with the most significant bit of the destination operand). The
destination operand can be a register or a memory location; the source operand is a register. The
count operand is an unsigned integer that can be an immediate byte or the contents of the CL
register. Only bits 0 through 4 of the count are used, which masks the count to a value between
0 and 31. If the count is greater than the operand size, the result in the destination operand is
undefined.
If the count is one or greater, the CF flag is filled with the last bit shifted out of the destination
operand. For a 1-bit shift, the OF flag is set if a sign change occurred; otherwise, it is cleared. If
the count operand is 0, the flags are not affected.
The SHRD instruction is useful for multiprecision shifts of 64 bits or more.
Opcode
Instruction
Description
0F AC
SHRD r/m16,r16,imm8Shift r/m16 to right imm8 places while shifting bits from
r16 in from the left
0F AD
SHRD r/m16,r16,CLShift r/m16 to right CL places while shifting bits from r16
in from the left
0F AC
SHRD r/m32,r32,imm8Shift r/m32 to right imm8 places while shifting bits from
r32 in from the left
0F AD
SHRD r/m32,r32,CLShift r/m32 to right CL places while shifting bits from r32
in from the left
