Cryptographic Instructions

Working Registers

The first 16 registers of the Co-processor register set are working registers. Working Registers are available to all operations. Registers 16-31 are scratch registers. These can be accessed by MOV, CRMOV, CRLD, and CRST, and by CRADD, CRSUB, CROR, CRXOR, CRAND, and CRANDN.

Functions

Copy/Load

Comparison

Bits:

• d: Destination Register
• a: First working register to compare
• b: Second working register to compare
• r: Overwrite Condition Mask
• t: Test (0: Equals, 1: Similarity, 2: Difference, 3: Not Equal)

Behaviour: Tests a and b according to t, modifying d accordingly. If r is set, d is set to the result. If r is clear, d is set to the result anded with the current value of d. For test 0, the result is all 1s if they are equal, and all 0s if they are different. For Test 1, sets the nth bit to 1 if and only if that bit is the same between a and b. For Test 2, sets the nth bit to 1 if and only if that bit is different between a and b. For test 3, the result is all 1s if the values are different.

This instruction is guaranteed to have consistent timing regardless of the input values of d, a, or b.