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Implement bitwise shifting #251

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merged 6 commits into from
Jul 24, 2018
Merged

Implement bitwise shifting #251

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85aad21
Add SHL/SHR/SAR opcodes
axic Jan 26, 2018
ed6b9dc
Implement SHL and SHR
axic Jan 26, 2018
6218bc6
Check if constantinople hard fork is active in the SHL/SHR/SAR implem…
axic Jul 20, 2018
4c64288
Implement SAR
axic Jul 23, 2018
b90ba6e
Always properly throw VMError
axic Jul 23, 2018
d843cd2
Optimise SAR to not use from/toTwos conversion
axic Jul 23, 2018
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39 changes: 39 additions & 0 deletions lib/opFns.js
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,45 @@ module.exports = {

return new BN(word.shrn((31 - pos.toNumber()) * 8).andln(0xff))
},
SHL: function (a, b, runState) {
if (!runState._common.gteHardfork('constantinople')) {
trap(ERROR.INVALID_OPCODE)
}
if (a.gten(256)) {
return new BN(0)
}
return b.shln(a.toNumber()).iand(utils.MAX_INTEGER)
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https://github.com/ethereum/EIPs/blob/master/EIPS/eip-145.md#0x1b-shl-shift-left

I am not super-fluent on bit operations, but I think I have found all conditions from the EIP in the implementation.

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(always a bit shaky on this signed/unsigned stuff)

},
SHR: function (a, b, runState) {
if (!runState._common.gteHardfork('constantinople')) {
trap(ERROR.INVALID_OPCODE)
}
if (a.gten(256)) {
return new BN(0)
}
return b.shrn(a.toNumber())
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https://github.com/ethereum/EIPs/blob/master/EIPS/eip-145.md#0x1c-shr-logical-shift-right

Same for SHR.

},
SAR: function (a, b, runState) {
if (!runState._common.gteHardfork('constantinople')) {
trap(ERROR.INVALID_OPCODE)
}
const isSigned = b.testn(255)
if (a.gten(256)) {
if (isSigned) {
return new BN(utils.MAX_INTEGER)
} else {
return new BN(0)
}
}
const c = b.shrn(a.toNumber())
if (isSigned) {
const shiftedOutWidth = 255 - a.toNumber()
const mask = utils.MAX_INTEGER.shrn(shiftedOutWidth).shln(shiftedOutWidth)
return c.ior(mask)
} else {
return c
}
},
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https://github.com/ethereum/EIPs/blob/master/EIPS/eip-145.md#0x1d-sar-arithmetic-shift-right

I also think I can roughly follow what is going on here and think all EIP conditions are covered and can also place all - this to me appearing a bit esoteric - mask stuff to the places in the EIP. Would have to do an extra hour of bit operation reading though for a better understanding.

Since tests are passing I will approve.

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@axic axic Jul 24, 2018 •
edited
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Here the point is to fill the top with set bits, that is achieved by ORing the mask. The mask is then created by taking an all bits set input (MAX_INTEGER) and making sure the bottom part where actual data remainded is 0.

// 0x20 range - crypto
SHA3: function (offset, length, runState) {
var data = memLoad(runState, offset, length)
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3 changes: 3 additions & 0 deletions lib/opcodes.js
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Expand Up @@ -26,6 +26,9 @@ const codes = {
0x18: ['XOR', 3, 2, 1, false],
0x19: ['NOT', 3, 1, 1, false],
0x1a: ['BYTE', 3, 2, 1, false],
0x1b: ['SHL', 3, 2, 1, false],
0x1c: ['SHR', 3, 2, 1, false],
0x1d: ['SAR', 3, 2, 1, false],

// 0x20 range - crypto
0x20: ['SHA3', 30, 2, 1, false],
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4 changes: 2 additions & 2 deletions lib/runCode.js
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Expand Up @@ -213,14 +213,14 @@ module.exports = function (opts, cb) {
if (result !== undefined) {
if (retNum !== 1) {
// opcode post-stack mismatch
return cb(VmError(ERROR.INTERNAL_ERROR))
return cb(new VmError(ERROR.INTERNAL_ERROR))
}

runState.stack.push(result)
} else {
if (!opInfo.async && retNum !== 0) {
// opcode post-stack mismatch
return cb(VmError(ERROR.INTERNAL_ERROR))
return cb(new VmError(ERROR.INTERNAL_ERROR))
}
}

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