How to sum two float4 arrays values into a Datum array? (c function in postgres)

My question is about C functions in PostgreSQL, where I'm trying to receive 2 float4[] arrays as parameters and return a float4[] array as the sum of array1 + array2 (columns in tables are set as float4[] as well), but can't achieve it:

To create the function:

CREATE OR REPLACE FUNCTION sum(float4[], float4[]) RETURNS float4[]
AS 'example.so', 'sum'
LANGUAGE C STRICT;
-- 'example.so' is already on /usr/lib/postgresql/9.1/lib

And the C code:

Datum sumar(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(sumar);
Datum sumar(PG_FUNCTION_ARGS)

{
  ArrayType *array1, *array2;

  // The array element types:
  Oid arrayElementType1, arrayElementType2;

  // The array element type widths:
  int16 arrayElementTypeWidth1, arrayElementTypeWidth2;

  // The array element type:
  bool arrayElementTypeByValue1, arrayElementTypeByValue2;

  // The array element type alignment codes:
  char arrayElementTypeAlignmentCode1, arrayElementTypeAlignmentCode2;

  // The array contents, as PostgreSQL "datum" objects:
  Datum *arrayContent1, *arrayContent2;

  // List of "is null" flags for the array contents:
  bool *arrayNullFlags1, *arrayNullFlags2;

  // The size of each array:
  int arrayLength1, arrayLength2;

  Datum *sumContent;
  int i;
  ArrayType* resultArray;

  // Extract the PostgreSQL arrays from the parameters passed to this function call.
  array1 = PG_GETARG_ARRAYTYPE_P(0);
  array2 = PG_GETARG_ARRAYTYPE_P(1);

  // Determine the array element types.
  arrayElementType1 = ARR_ELEMTYPE(array1);
  get_typlenbyvalalign(arrayElementType1, &arrayElementTypeWidth1, &arrayElementTypeByValue1, &arrayElementTypeAlignmentCode1);
  arrayElementType2 = ARR_ELEMTYPE(array2);
  get_typlenbyvalalign(arrayElementType2, &arrayElementTypeWidth2, &arrayElementTypeByValue2, &arrayElementTypeAlignmentCode2);

  // Extract the array contents (as Datum objects).
  deconstruct_array(array1, arrayElementType1, arrayElementTypeWidth1, arrayElementTypeByValue1, arrayElementTypeAlignmentCode1, &arrayContent1, &arrayNullFlags1, &arrayLength1);
  deconstruct_array(array2,arrayElementType2, arrayElementTypeWidth2, arrayElementTypeByValue2, arrayElementTypeAlignmentCode2, &arrayContent2, &arrayNullFlags2, &arrayLength2);

  //Create a new array of sum results (as Datum objects).
  sumContent = (Datum *) palloc(sizeof(Datum) * arrayLength1);

  // Generate the sums.
  for (i = 0; i < arrayLength1; i++)
  {
    sumContent[i] =  arrayContent1[i] + arrayContent2[i];
  }

  // Wrap the sums in a new PostgreSQL array object.
  resultArray = construct_array(sumContent, arrayLength1, arrayElementType1, arrayElementTypeWidth1, arrayElementTypeByValue1, arrayElementTypeAlignmentCode1);

  // Return the final PostgreSQL array object.
  PG_RETURN_ARRAYTYPE_P(resultArray);
}

When it returns the array at the ends, it shows me just negative values (the sum is wrong), but when I pass 2 int arrays it works fine. Also I have tried casting the values before the sum, just like:

sumContent[i] =  Float4GetDatum(arrayContent1[i]) + Float4GetDatum(arrayContent2[i];)

and

sumContent[i] =  DatumGetFloat4arrayContent1[i]) + DatumGetFloat4(arrayContent2[i]);

but it keeps giving me strange values.