# P-Ext ISA

[[!toc ]]

# 16-bit Arithmetic

| Mnemonic           | 16-bit Instruction        | Simple-V Equivalent |
| ------------------ | ------------------------- | ------------------- |
| ADD16 rt, ra, rb   | add                       | RV ADD (bitwidth=16) |
| RADD16 rt, ra, rb  | Signed Halving add        | |
| URADD16 rt, ra, rb | Unsigned Halving add      | |
| KADD16 rt, ra, rb  | Signed Saturating add     | |
| UKADD16 rt, ra, rb | Unsigned Saturating add   | |
| SUB16 rt, ra, rb   | sub                       | RV SUB (bitwidth=16) |
| RSUB16 rt, ra, rb  | Signed Halving sub        | |
| URSUB16 rt, ra, rb | Unsigned Halving sub                | |
| KSUB16 rt, ra, rb  | Signed Saturating sub               | |
| UKSUB16 rt, ra, rb | Unsigned Saturating sub             | |
| CRAS16 rt, ra, rb  | Cross Add & Sub                     | |
| RCRAS16 rt, ra, rb | Signed Halving Cross Add & Sub      | |
| URCRAS16 rt, ra, rb| Unsigned Halving Cross Add & Sub    | |
| KCRAS16 rt, ra, rb | Signed Saturating Cross Add & Sub   | |
| UKCRAS16 rt, ra, rb| Unsigned Saturating Cross Add & Sub | |
| CRSA16 rt, ra, rb  | Cross Sub & Add                     | |
| RCRSA16 rt, ra, rb | Signed Halving Cross Sub & Add      | |
| URCRSA16 rt, ra, rb| Unsigned Halving Cross Sub & Add    | |
| KCRSA16 rt, ra, rb | Signed Saturating Cross Sub & Add   | |
| UKCRSA16 rt, ra, rb| Unsigned Saturating Cross Sub & Add | |

# 8-bit Arithmetic

| Mnemonic           | 16-bit Instruction        | Simple-V Equivalent |
| ------------------ | ------------------------- | ------------------- |
| ADD8 rt, ra, rb    | add                       | RV ADD (bitwidth=8)|
| RADD8 rt, ra, rb   | Signed Halving add        | |
| URADD8 rt, ra, rb  | Unsigned Halving add      | |
| KADD8 rt, ra, rb   | Signed Saturating add     | |
| UKADD8 rt, ra, rb  | Unsigned Saturating add   | |
| SUB8 rt, ra, rb    | sub                       | RV SUB (bitwidth=8)|
| RSUB8 rt, ra, rb   | Signed Halving sub        | |
| URSUB8 rt, ra, rb  | Unsigned Halving sub      | |