Requires Microsoft Macro Assembler (MASM)

feverish.asm

.386					; compiled for Intel 80386 or later and 32-bit instructions and addressing should be used.
.model flat,stdcall			; memory is a single contiguous address space and use standard calling convention of procedures.
.stack 4096				; reserve 4096 bytes for the "stack".
ExitProcess PROTO dwExitCode:DWORD	; prototype of "ExitProcess" procedure has the parameter of a DWORD "dWExitCode".

.data
; <variable_name> <variable_type> <variable_value>
farenheit REAL4 170.0		; REAL4 is a 4-byte (32-bits) floating-point number.
THIRTY_TWO REAL4 32.0
FIVE REAL4 5.0
NINE REAL4 9.0
celcius REAL4 ?			; ? is uninitilized and can contain anything which was there or not there previously (garbage value).
FEVERISH_CUT_OFF REAL4 37.5
result DWORD ?			; DWORD is a 4-byte (32-bits) unsigned integer. it stands for DOUBLE WORD because a WORD is 16-bits.

.code
main PROC			; marks the start of the procedure named "main". <procedure_name> PROC
	FINIT			; initialize FPU.

	; step 1. convert farenheit to celcius

	FLD farenheit    	; load value of "farenheit".
	FSUB THIRTY_TWO 	; subtract 32 from FPU.
	FMUL FIVE       	; multiply FPU by 5.
	FDIV NINE       	; divide FPU by 9.
	FSTP celcius   		; store FPU into "celcius".
	
	; step 2. determine if the temperature is feverish.

	mov result,1   		; assume feverish

	FLD celcius		; reload "celcius" into the FPU. remember, FSTP is destructive, destroying the FPU stack after storing.
	FCOM FEVERISH_CUT_OFF	; compare FPU with the variable "FEVERISH_CUT_OFF".

				; by setting the FLAGS register, we can use conditional jumps like JAE (Jump if Above or Equal).
	FSTSW AX		; store FPU status word into the AX (16-bit accumulator) register.
	SAHF			; store AH (high byte of the AX register) into the lower byte of the FLAGS register.

	JAE hasFever    	; if above or equal, jump to the label "hasFever".
	mov result,0    	; else, we assumed wrong and load 0 into result.

hasFever:			; labels a location we can jump to. <label_name>:
	INVOKE ExitProcess,0	; invoke is a high-level macro provided to simplify calling and procedures.
main ENDP			; marks the end of procedure named "main". <procedure_name> ENDP

END main	; end of the source file and specifies that the procedure "main" is the entry point. END <entry_point_name>