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Cycle Timings and Interlock Behavior
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 14-14
ID013010 Non-Confidential, Unrestricted Access
14.8 Divide
This section describes the cycle timing behavior of the
UDIV
and
SDIV
instructions.
The divider unit is separate to the main execute pipeline so the
UDIV
and
SDIV
instructions require
one cycle to issue. They execute out-of-order relative to the rest of the pipeline, and require an
additional issue cycle at the end of the divide operation to write the result to the destination
register. This additional cycle is not required if the divide instruction fails its condition code.
Result Latency for a
UDIV
instruction A divided by B is given by:
Result Latency for a
SDIV
instruction A divided by B is given by:
Note
• A divide instruction that fails its condition code or attempts to divide by zero has a Result
Latency of three.
• The value of the (clz(B) - clz(A) + 1)/2 component of these equations must be rounded
down.
• The clz(x) function counts the number of leading zeros in the 32-bit value x. If x is
negative, it is negated before this count occurs.
2
clz(B) - clz(A) + 1
,0
Result latency = 3 +
max
())(
2
clz(B) - clz(A) + 1
,0
Result latency = 4 +
max
())(