Update bigint_modexp.md

EIPS/bigint_modexp.md

@@ -8,7 +8,7 @@ At address 0x00......05, add a precompile that expects input in the following fo
 
  <length of BASE> <BASE> <length of EXPONENT> <EXPONENT> <length of MODULUS> <MODULUS>
 
-Where every length is a 32-byte left-padded integer representing the number of bytes to be taken up by the next value. Consumes `floor(length(MODULUS)**2 * length(EXPONENT) / GQUADDIVISOR)` gas. If there is enough gas, returns an output as a byte array with the same length as the modulus.
+Where every length is a 32-byte left-padded integer representing the number of bytes to be taken up by the next value. If the input cannot be fully parsed in this way (ie. attempting to parse it in this way either tries to consume more call data than is given or leaves some call data unused), then it throws an exception. Also, throws if `BASE >= MODULUS`. Otherwise, consumes `floor(length(MODULUS)**2 * length(EXPONENT) / GQUADDIVISOR)` gas, and if there is enough gas, returns an output `BASE**EXPONENT % MODULUS` as a byte array with the same length as the modulus.
 
 For example, the input data:
 
@@ -25,6 +25,16 @@ Represents the exponent `3**(2**256 - 2**32 - 978) % (2**256 - 2**32 - 977)`. By
 
 Returned as 32 bytes because the modulus length was 32 bytes. The gas cost would be `32**2 * 32 / 20 = 1638` gas (note that this roughly equals the cost of using the EXP opcode to compute a 32-byte exponent). A 4096-bit RSA exponentiation would cost `256**2 * 256 / 20 = 838860` gas in the worst case, though RSA verification in practice usually uses an exponent of 3 or 65537, which would reduce the gas consumption to 3276 or 6553, respectively.
 
+This input data:
+
+ 0000000000000000000000000000000000000000000000000000000000000000
+ 0000000000000000000000000000000000000000000000000000000000000020
+ fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2e
+ 0000000000000000000000000000000000000000000000000000000000000020
+ fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f
+
+Would 
+
 ### Rationale
 
 This allows for efficient RSA verification inside of the EVM, as well as other forms of number theory-based cryptography. Note that adding precompiles for addition and subtraction is not required, as the in-EVM algorithm is efficient enough, and multiplication can be done through this precompile via `a * b = ((a + b)**2 - (a - b)**2) / 4`.