Use Efficient Data Types

In cases where more than one data type can be used for a variable, consider selecting the data types based on the following hierarchy, listed from most to least efficient:

• On ia32 systems:
  
  • Integer of four bytes, expressed as INTEGER(4) or INTEGER*4
  • Single-precision real, expressed explicitly as REAL, REAL(KIND=4), or REAL*4
  • Double-precision real, expressed explicitly as DOUBLE PRECISION, REAL(KIND=8), or REAL*8
  • Integer of eight bytes, expressed as INTEGER(8) or INTEGER*8
• On ia64 systems:
  • Integer of four or eight bytes (also see Avoid Small Integer and Small Logical Data Items (ia64 only))
  • Single-precision real, expressed explicitly as REAL, REAL(KIND=4), or REAL*4
  • Double-precision real, expressed explicitly as DOUBLE PRECISION, REAL(KIND=8), or REAL*8

However, keep in mind that in an arithmetic expression, you should avoid mixing integer and floating-point (REAL) data (see Avoid Mixed Data Type Arithmetic Expressions).