This item is about CODE/EDOC when compiling in 32-bit mode. For a discussion of 64-bit CODE/EDOC see here.
The CODE statement switches the compiler into a mode in which it accepts Intel 32-bit assembler instructions rather than Fortran statements. The compiler is returned to normal by the EDOC statement. A CODE/EDOC sequence may appear anywhere that an executable Fortran statement is permitted. For example:
LEA EDI%,L ;EDI gets address of L
MOVB AL%,='*' ;Asterix in AL
MOV ECX%,=10 ;Count in ECX
REP ;Rep prefix coded as
+ ; a separate instruction
STOSB ;This fills L with aster isks
JMP $10 ;Jump to label 10
PRINT *,'This should not be printed'
10 PRINT *,'L = ',L
This example is artificial in that there is no real point in performing operations in assembler that can be done in Fortran, however it illustrates that code is written according to the following conventions:
Instructions refer to Fortran objects or explicitly to the registers
Register names are followed by a '%' to distinguish them unambiguously from variable names.
Instructions must start in column 7 or beyond.
Only numeric (Fortran) labels are permitted.
Comments may be included provided they are preceded by a semi-colon character (;)
Some mnemonics are followed by an 'H' to indicate halfword (16-bit) operation or by 'B' to indicate a byte operation. This is discussed in more detail below.