rsubl - 2024.2 English

Description

The contents of register rA_L are subtracted from the contents of register rB_L and the result is placed into register rD_L. Bit 3 of the instruction (labeled as K in the figure) is set to one for the mnemonic rsublk. Bit 4 of the instruction (labeled as C in the figure) is set to one for the mnemonic rsublc. Both bits are set to one for the mnemonic rsublkc.

When an rsubl instruction has bit 3 set (rsublk, rsublkc), the carry flag will Keep its previous value regardless of the outcome of the execution of the instruction. If bit 3 is cleared (rsubl, rsublc), then the carry flag will be affected by the execution of the instruction.

When bit 4 of the instruction is set to one (rsublc, rsublkc), the content of the carry flag (MSR[C]) affects the execution of the instruction. When bit 4 is cleared (rsubl, rsublk), the content of the carry flag does not affect the execution of the instruction (providing a normal subtraction).

Pseudocode

if C = 0 then
   (rDL) ← (rBL) + (rAL) + 1
else
   (rDL) ← (rBL) + (rAL) + MSR[C]
if K = 0 then
   MSR[C] ← CarryOut64

Registers Altered

• rD_L
• MSR[C]

Latency

• 1 cycle

Notes

• In subtractions, Carry = (Borrow). When the Carry is set by a subtraction, it means that there is no Borrow, and when the Carry is cleared, it means that there is a Borrow.