From cee0a38278de07ff853c4071bde67362436fd069 Mon Sep 17 00:00:00 2001
From: andri lim <jangko128@gmail.com>
Date: Thu, 25 Apr 2019 22:33:26 +0700
Subject: [PATCH] add some comment

---
 nimbus/vm/interpreter/opcodes_impl.nim |  5 +++++
 nimbus/vm/precompiles.nim              | 21 +++++++++++++++++++++
 tests/test_generalstate_failing.nim    |  3 +++
 3 files changed, 29 insertions(+)

diff --git a/nimbus/vm/interpreter/opcodes_impl.nim b/nimbus/vm/interpreter/opcodes_impl.nim
index 76e5e9b31..0861b0bc9 100644
--- a/nimbus/vm/interpreter/opcodes_impl.nim
+++ b/nimbus/vm/interpreter/opcodes_impl.nim
@@ -197,6 +197,11 @@ op sha3, inline = true, startPos, length:
   ## 0x20, Compute Keccak-256 hash.
   let (pos, len) = (startPos.toInt, length.toInt)
 
+  # TODO:
+  # "randomStatetest14.json", # SHA3 offset
+  # "sha3_deja.json", # SHA3 startPos
+  # both test require Uint256 to calculate startpos/offset
+
   if pos < 0 or len < 0 or pos > 2147483648:
     raise newException(OutOfBoundsRead, "Out of bounds memory access")
 
diff --git a/nimbus/vm/precompiles.nim b/nimbus/vm/precompiles.nim
index 467ab1137..c69c59ff2 100644
--- a/nimbus/vm/precompiles.nim
+++ b/nimbus/vm/precompiles.nim
@@ -56,6 +56,24 @@ proc getPoint[T: G1|G2](t: typedesc[T], data: openarray[byte]): Point[T] =
     raise newException(ValidationError, "Could not get point value")
   if not py.fromBytes2(data.toOpenArray(nextOffset, nextOffset * 2 - 1)):
     raise newException(ValidationError, "Could not get point value")
+
+  # "ecpairing_perturb_g2_by_field_modulus_again.json",
+  # "ecpairing_perturb_zeropoint_by_field_modulus.json",
+  # "ecpairing_perturb_g2_by_field_modulus.json",
+  # modulus comparion in FQ2.fromBytes produce different result
+  const
+    modulus = Uint256.fromHex("30644e72e131a029b85045b68181585d97816a916871ca8d3c208c16d87cfd47")
+  let a = Uint256.fromBytesBE(data.toOpenArray(0, 31), false)
+  let b = Uint256.fromBytesBE(data.toOpenArray(32, 63), false)
+  when T is G2:
+    let c = Uint256.fromBytesBE(data.toOpenArray(64, 95), false)
+    let d = Uint256.fromBytesBE(data.toOpenArray(96, 127), false)
+    if a >= modulus or b >= modulus or c >= modulus or d >= modulus:
+      raise newException(ValidationError, "value greater than field modulus")
+  else:
+    if a >= modulus or b >= modulus:
+      raise newException(ValidationError, "value greater than field modulus")
+
   if px.isZero() and py.isZero():
     result = T.zero()
   else:
@@ -138,6 +156,7 @@ proc modExpInternal(computation: BaseComputation, base_len, exp_len, mod_len: in
         else: log2(exp)    # highest-bit in exponent
       else:
         let first32 = rawMsg.rangeToPadded[:Uint256](96 + base_len, 95 + base_len + exp_len)
+        # TODO: `modexpRandomInput.json` require Uint256 arithmetic for this code below
         if not first32.isZero:
           8 * (exp_len - 32) + first32.log2
         else:
@@ -176,6 +195,8 @@ proc modExpInternal(computation: BaseComputation, base_len, exp_len, mod_len: in
                  else:
                     powmod(base, exp, modulo).toByteArrayBE
 
+    # maximum output len is the same as mod_len
+    # if it less than mod_len, it will be zero padded at left
     if output.len >= mod_len:
       computation.rawOutput = @(output[^mod_len..^1])
     else:
diff --git a/tests/test_generalstate_failing.nim b/tests/test_generalstate_failing.nim
index 4b4b60790..239eb02e5 100644
--- a/tests/test_generalstate_failing.nim
+++ b/tests/test_generalstate_failing.nim
@@ -25,10 +25,13 @@ func allowedFailingGeneralStateTest*(folder, name: string): bool =
     "RevertInCreateInInit.json",
     "modexp.json",
 
+    # see precompiles getPoint[G2]
     "ecpairing_perturb_g2_by_field_modulus_again.json",
     "ecpairing_perturb_zeropoint_by_field_modulus.json",
     "ecpairing_perturb_g2_by_field_modulus.json",
 
+    # all these tests below actually pass
+    # but they are very slow
     # byzantium slow
     "LoopCallsDepthThenRevert3.json",
     "LoopCallsDepthThenRevert2.json",