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Feature: bit count via math.bits library #42

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merged 1 commit into from
Sep 10, 2023
Merged

Feature: bit count via math.bits library #42

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40 changes: 22 additions & 18 deletions pkg/vm/instruction.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ package vm

import (
"fmt"
"math/bits"

f "github.com/consensys/gnark-crypto/ecc/stark-curve/fp"
)
Expand Down Expand Up @@ -155,13 +156,13 @@ func decodeInstructionFlags(instruction *Instruction, flags uint16) error {
instruction.DstRegister = Register((flags >> dstRegBit) & 1)
instruction.Op0Register = Register((flags >> op0RegBit) & 1)

op1Addr, err := oneHot((flags>>op1ImmBit)&1, (flags>>op1FpBit)&1, (flags>>op1ApBit)&1)
op1Addr, err := oneHot(flags&(1<<op1ImmBit|1<<op1FpBit|1<<op1ApBit), op1ImmBit, 3)
if err != nil {
return fmt.Errorf("error decoding op1_addr of instruction: %w", err)
}
instruction.Op1Source = Op1Src(op1Addr)

pcUpdate, err := oneHot((flags>>pcJumpAbsBit)&1, (flags>>pcJumpRelBit)&1, (flags>>pcJnzBit)&1)
pcUpdate, err := oneHot(flags&(1<<pcJumpAbsBit|1<<pcJumpRelBit|1<<pcJnzBit), pcJumpAbsBit, 3)
if err != nil {
return fmt.Errorf("error decoding pc_update of instruction: %w", err)
}
Expand All @@ -177,7 +178,7 @@ func decodeInstructionFlags(instruction *Instruction, flags uint16) error {
defaultResLogic = Op1
}

res, err := oneHot((flags>>resAddBit)&1, (flags>>resMulBit)&1)
res, err := oneHot(flags&(1<<resAddBit|1<<resMulBit), resAddBit, 2)
if err != nil {
return fmt.Errorf("error decoding res_logic of instruction: %w", err)
}
Expand All @@ -188,13 +189,13 @@ func decodeInstructionFlags(instruction *Instruction, flags uint16) error {
instruction.Res = ResLogic(res)
}

apUpdate, err := oneHot((flags>>apAddBit)&1, (flags>>apAdd1Bit)&1)
apUpdate, err := oneHot(flags&(1<<apAddBit|1<<apAdd1Bit), apAddBit, 2)
if err != nil {
return fmt.Errorf("error decoding ap_update of instruction: %w", err)
}
instruction.ApUpdate = ApUpdate(apUpdate)

opcode, err := oneHot((flags>>opcodeCallBit)&1, (flags>>opcodeRetBit)&1, (flags>>opcodeAssertEqBit)&1)
opcode, err := oneHot(flags&(1<<opcodeCallBit|1<<opcodeRetBit|1<<opcodeAssertEqBit), opcodeCallBit, 3)
if err != nil {
return fmt.Errorf("error decoding opcode of instruction: %w", err)
}
Expand Down Expand Up @@ -223,25 +224,28 @@ func decodeInstructionFlags(instruction *Instruction, flags uint16) error {
return nil
}

// Given []uint16 of 0s or 1s returns the set bit if there's only one such
// and return len(bits) in case there's no set bits.
// Given a uint16 returns the set bit offset by offset if there's only one such
// and return maxLen in case there's no set bits.
// If there are more than 1 set bits return an error.
func oneHot(bits ...uint16) (uint16, error) {
var checkSum uint16 = 0
setBit := len(bits)
func oneHot(bin, offset, maxLen uint16) (uint16, error) {
numberOfBits := bits.OnesCount16(bin)

// checking
for i, bit := range bits {
checkSum += bit
if numberOfBits > 1 {
digits := make([]uint8, 0, maxLen)
bin = bin >> offset

if bit == 1 {
setBit = i
for i := 0; i < int(maxLen); i++ {
digits = append(digits, uint8(bin%2))
bin >>= 1
}
return 0, fmt.Errorf("decoding wrong sequence of bits: %b", digits)
}

if checkSum > 1 {
return 0, fmt.Errorf("decoding wrong sequence of bits: %v", bits)
len := bits.Len16(bin)

if len == 0 {
return maxLen, nil
}

return uint16(setBit), nil
return uint16(len-int(offset)) - 1, nil
}