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workaround Clang and empty {.goto.} branches
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@mratsim
mratsim committed Sep 17, 2023
1 parent f6f5c1f commit cc5c175
Showing 1 changed file with 22 additions and 36 deletions.
58 changes: 22 additions & 36 deletions constantine/ethereum_eip4844_kzg_polynomial_commitments.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -214,14 +214,12 @@ func blob_to_field_polynomial(
#
# We use a simple goto state machine to handle errors and cleanup (if allocs were done)
# and have 2 different checks:
# - Either we are in "defaultPath(state)" section that shortcuts to resource cleanup on error
# - Either we are in "HappyPath" section that shortcuts to resource cleanup on error
# - or there are no resources to clean and we can early return from a function.

template check(evalExpr: CttCodecScalarStatus): untyped {.dirty.} =
# Translate codec status code to KZG status code
# Beware of resource cleanup like heap allocation, this can early exit the caller.
when declared(usingGotos): # TODO: this unfortunately doesn't work
{.error: "Using early return 'check' when resource cleanup might be needed after errors.".}
block:
let status = evalExpr # Ensure single evaluation
case status
Expand All @@ -232,8 +230,6 @@ template check(evalExpr: CttCodecScalarStatus): untyped {.dirty.} =
template check(evalExpr: CttCodecEccStatus): untyped {.dirty.} =
# Translate codec status code to KZG status code
# Beware of resource cleanup like heap allocation, this can early exit the caller.
when declared(usingGotos): # TODO: this unfortunately doesn't work
{.error: "Using early return 'check' when resource cleanup might be needed after errors.".}
block:
let status = evalExpr # Ensure single evaluation
case status
Expand All @@ -244,37 +240,27 @@ template check(evalExpr: CttCodecEccStatus): untyped {.dirty.} =
of cttCodecEcc_PointNotInSubgroup: return cttEthKZG_EccPointNotInSubGroup
of cttCodecEcc_PointAtInfinity: discard

type JumpTarget = enum
JumpToComputing, JumpToExiting

template defaultPath(state, body: untyped): untyped =
const usingGotos {.used.} = true
var state {.goto.} = JumpToComputing
case state
of JumpToComputing:
body
of JumpToExiting:
discard

template check(state: untyped, evalExpr: CttCodecScalarStatus): untyped =
template check(Section: untyped, evalExpr: CttCodecScalarStatus): untyped {.dirty.} =
# Translate codec status code to KZG status code
# Exit current code block
block:
let status = evalExpr # Ensure single evaluation
case status
of cttCodecScalar_Success: discard
of cttCodecScalar_Zero: discard
of cttCodecScalar_ScalarLargerThanCurveOrder: result = cttEthKZG_EccPointNotInSubGroup; state = JumpToExiting
of cttCodecScalar_ScalarLargerThanCurveOrder: result = cttEthKZG_EccPointNotInSubGroup; break Section

template check(state: untyped, evalExpr: CttCodecEccStatus): untyped =
template check(Section: untyped, evalExpr: CttCodecEccStatus): untyped {.dirty.} =
# Translate codec status code to KZG status code
# Exit current code block
block:
let status = evalExpr # Ensure single evaluation
case status
of cttCodecEcc_Success: discard
of cttCodecEcc_InvalidEncoding: result = cttEthKZG_EccInvalidEncoding; state = JumpToExiting
of cttCodecEcc_CoordinateGreaterThanOrEqualModulus: result = cttEthKZG_EccCoordinateGreaterThanOrEqualModulus; state = JumpToExiting
of cttCodecEcc_PointNotOnCurve: result = cttEthKZG_EccPointNotOnCurve; state = JumpToExiting
of cttCodecEcc_PointNotInSubgroup: result = cttEthKZG_EccPointNotInSubGroup; state = JumpToExiting
of cttCodecEcc_InvalidEncoding: result = cttEthKZG_EccInvalidEncoding; break Section
of cttCodecEcc_CoordinateGreaterThanOrEqualModulus: result = cttEthKZG_EccCoordinateGreaterThanOrEqualModulus; break Section
of cttCodecEcc_PointNotOnCurve: result = cttEthKZG_EccPointNotOnCurve; break Section
of cttCodecEcc_PointNotInSubgroup: result = cttEthKZG_EccPointNotInSubGroup; break Section
of cttCodecEcc_PointAtInfinity: discard

func blob_to_kzg_commitment*(
Expand All @@ -300,8 +286,8 @@ func blob_to_kzg_commitment*(

let poly = allocHeapAligned(PolynomialEval[FIELD_ELEMENTS_PER_BLOB, matchingOrderBigInt(BLS12_381)], 64)

defaultPath(state):
check state, poly.blob_to_bigint_polynomial(blob)
block HappyPath:
check HappyPath, poly.blob_to_bigint_polynomial(blob)

var r {.noinit.}: ECP_ShortW_Aff[Fp[BLS12_381], G1]
kzg_commit(r, poly.evals, ctx.srs_lagrange_g1) # symbol resolution need explicit generics
Expand Down Expand Up @@ -338,9 +324,9 @@ func compute_kzg_proof*(

let poly = allocHeapAligned(PolynomialEval[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], 64)

defaultPath(state):
block HappyPath:
# Blob -> Polynomial
check state, poly.blob_to_field_polynomial(blob)
check HappyPath, poly.blob_to_field_polynomial(blob)

# KZG Prove
var y {.noInit.}: Fr[BLS12_381] # y = p(z), eval at challenge z
Expand Down Expand Up @@ -402,9 +388,9 @@ func compute_blob_kzg_proof*(
# Blob -> Polynomial
let poly = allocHeapAligned(PolynomialEval[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], 64)

defaultPath(state):
block HappyPath:
# Blob -> Polynomial
check state, poly.blob_to_field_polynomial(blob)
check HappyPath, poly.blob_to_field_polynomial(blob)

# Fiat-Shamir challenge
var challenge {.noInit.}: Fr[BLS12_381]
Expand Down Expand Up @@ -443,9 +429,9 @@ func verify_blob_kzg_proof*(
let poly = allocHeapAligned(PolynomialEval[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], 64)
let invRootsMinusZ = allocHeapAligned(array[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], alignment = 64)

defaultPath(state):
block HappyPath:
# Blob -> Polynomial
check state, poly.blob_to_field_polynomial(blob)
check HappyPath, poly.blob_to_field_polynomial(blob)

# Fiat-Shamir challenge
var challengeFr {.noInit.}: Fr[BLS12_381]
Expand Down Expand Up @@ -520,10 +506,10 @@ func verify_blob_kzg_proof_batch*(
let poly = allocHeapAligned(PolynomialEval[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], alignment = 64)
let invRootsMinusZ = allocHeapAligned(array[FIELD_ELEMENTS_PER_BLOB, Fr[BLS12_381]], alignment = 64)

defaultPath(state):
block HappyPath:
for i in 0 ..< n:
check state, commitments[i].bytes_to_kzg_commitment(commitments_bytes[i])
check state, poly.blob_to_field_polynomial(blobs[i].addr)
check HappyPath, commitments[i].bytes_to_kzg_commitment(commitments_bytes[i])
check HappyPath, poly.blob_to_field_polynomial(blobs[i].addr)
challenges[i].fiatShamirChallenge(blobs[i], commitments_bytes[i])

# Lagrange Polynomial evaluation
Expand All @@ -544,7 +530,7 @@ func verify_blob_kzg_proof_batch*(
else:
evals_at_challenges[i].fromField(poly.evals[zIndex])

check state, proofs[i].bytes_to_kzg_proof(proof_bytes[i])
check HappyPath, proofs[i].bytes_to_kzg_proof(proof_bytes[i])

var randomBlindingFr {.noInit.}: Fr[BLS12_381]
block blinding: # Ensure we don't multiply by 0 for blinding
Expand Down

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