Don't use array[^1], it can throw and cannot be locally turn off

constantine/blssig_pop_on_bls12381_g2.nim

@@ -242,7 +242,7 @@ func deserialize_public_key_compressed_unchecked*(dst: var PublicKey, src: array
   # General case
   var t{.noInit.}: matchingBigInt(BLS12_381)
   t.unmarshal(src, bigEndian)
-  t.limbs[^1] = t.limbs[^1] and (MaxWord shr 3) # The first 3 bytes contain metadata to mask out
+  t.limbs[t.len-1] = t.limbs[t.len-1] and (MaxWord shr 3) # The first 3 bytes contain metadata to mask out
 
   if bool(t >= BLS12_381.Mod()):
     return cttBLS_CoordinateGreaterOrEqualThanModulus
@@ -296,7 +296,7 @@ func deserialize_signature_compressed_unchecked*(dst: var Signature, src: array[
   # General case
   var t{.noInit.}: matchingBigInt(BLS12_381)
   t.unmarshal(src.toOpenArray(0, 48-1), bigEndian)
-  t.limbs[^1] = t.limbs[^1] and (MaxWord shr 3) # The first 3 bytes contain metadata to mask out
+  t.limbs[t.limbs.len-1] = t.limbs[t.limbs.len-1] and (MaxWord shr 3) # The first 3 bytes contain metadata to mask out
 
   if bool(t >= BLS12_381.Mod()):
     return cttBLS_CoordinateGreaterOrEqualThanModulus

constantine/ethereum_evm_precompiles.nim

@@ -322,7 +322,7 @@ func eth_evm_ecpairing*(
   if N == 0:
     # Spec: "Empty input is valid and results in returning one."
     zeroMem(r.addr, r.sizeof())
-    r[^1] = byte 1
+    r[r.len-1] = byte 1
     return
 
   var gt0{.noInit.}, gt1{.noInit.}: Fp12[BN254_Snarks]
@@ -361,4 +361,4 @@ func eth_evm_ecpairing*(
 
   zeroMem(r.addr, r.sizeof())
   if gt0.isOne().bool:
-    r[^1] = byte 1
+    r[r.len-1] = byte 1

constantine/math/config/precompute.nim

@@ -236,7 +236,7 @@ func checkOdd(M: BigInt) =
 
 func checkValidModulus(M: BigInt) =
   const expectedMsb = M.bits-1 - WordBitWidth * (M.limbs.len - 1)
-  let msb = log2_vartime(BaseType(M.limbs[^1]))
+  let msb = log2_vartime(BaseType(M.limbs[M.limbs.len-1]))
 
   doAssert msb == expectedMsb, "Internal Error: the modulus must use all declared bits and only those:\n" &
     "    Modulus '" & M.toHex() & "' is declared with " & $M.bits &
@@ -254,7 +254,7 @@ func countSpareBits*(M: BigInt): int =
   ## - [0, 8p) if 3 bits are available
   ## - ...
   checkValidModulus(M)
-  let msb = log2_vartime(BaseType(M.limbs[^1]))
+  let msb = log2_vartime(BaseType(M.limbs[M.limbs.len-1]))
   result = WordBitWidth - 1 - msb.int
 
 func invModBitwidth[T: SomeUnsignedInt](a: T): T =
@@ -336,7 +336,7 @@ func r_powmod(n: static int, M: BigInt): BigInt =
     start = (w-1)*WordBitWidth + msb
     stop = n*WordBitWidth*w
 
-  result.limbs[^1] = SecretWord(BaseType(1) shl msb) # C0 = 2^(wn-1), the power of 2 immediatly less than the modulus
+  result.limbs[M.limbs.len-1] = SecretWord(BaseType(1) shl msb) # C0 = 2^(wn-1), the power of 2 immediatly less than the modulus
   for _ in start ..< stop:
     result.doubleMod(M)
 

helpers/prng_unsafe.nim

@@ -165,7 +165,7 @@ template clearExtraBitsOverMSB(a: var BigInt) =
   when a.bits != a.limbs.len * WordBitWidth:
     const posExtraBits = a.bits - (a.limbs.len-1) * WordBitWidth
     const mask = (One shl posExtraBits) - One
-    a.limbs[^1] = a.limbs[^1] and mask
+    a.limbs[a.limbs.len-1] = a.limbs[a.limbs.len-1] and mask
 
 func random_unsafe(rng: var RngState, a: var BigInt) =
   ## Initialize a standalone BigInt

research/kzg_poly_commit/fft_fr.nim

@@ -78,9 +78,9 @@ func expandRootOfUnity[F](rootOfUnity: F): seq[F] =
   result.setLen(2)
   result[0].setOne()
   result[1] = rootOfUnity
-  while not result[^1].isOne().bool:
+  while not result[result.len-1].isOne().bool:
     result.setLen(result.len + 1)
-    result[^1].prod(result[^2], rootOfUnity)
+    result[result.len-1].prod(result[result.len-2], rootOfUnity)
 
 # FFT Algorithm
 # ----------------------------------------------------------------

research/kzg_poly_commit/fft_g1.nim

@@ -82,10 +82,10 @@ func expandRootOfUnity[F](rootOfUnity: F): auto {.noInit.} =
   r[1] = rootOfUnity.toBig()
 
   var cur = rootOfUnity
-  while not r[^1].isOne().bool:
+  while not r[r.len-1].isOne().bool:
     cur *= rootOfUnity
     r.setLen(r.len + 1)
-    r[^1] = cur.toBig()
+    r[r.len-1] = cur.toBig()
 
   return r