How to implement math.h functions in Verilog

Contributed by
Chris Spear
Viewlogic Systems, Inc.




Here is a PLI 1.0 example. The code below shows a set of functions, used by their respective system calls. Together they achieve the same functionality that of their corresponding library function of math.h in C. (According to Chris, the hardest part of writing these system calls was to figure out how to return real type to the Verilog environment, rather than integer ).

This code has been created and run under VCS. For implementation using PLI2.0 in Verilog-XL, click here.


/*********************************************/
/* math.c - C routines for Verilog PLI */ 
#include "math.h" /* C Math routines */ 
#include "vcsuser.h" /* Base Verilog PLI definitions */ 
/* Definitions specific for math.c */ 
#define ARG1 1 /* First argument */ 
#define ARG2 2 /* Second argument */ 
#define RETURNV 0 /* Return value */ 
/****************************************************************/ 
/* Checktf() routine to check for a single real argument */ 
int math_check1() {
   if (tf_nump() != ARG1) { 
      tf_error("Wrong number of arguments, expecting 1"); 
      return; } 
   if (tf_typep(ARG1) != tf_readonlyreal && 
        tf_typep(ARG1) != tf_readwritereal) 
      tf_error("The argument must be a real number."); 
} 
/****************************************************************/ 
/* Checktf() routine to check for a single real argument */ 
int math_check2() { 
   if (tf_nump() != ARG2) { 
      tf_error("Wrong number of arguments, expecting 2"); return; 
   } 
   if (tf_typep(ARG1) != tf_readonlyreal && 
        tf_typep(ARG1) != tf_readwritereal) 
      tf_error("The first argument must be a real number."); 

   if (tf_typep(ARG2) != tf_readonlyreal && 
        tf_typep(ARG2) != tf_readwritereal) 
      tf_error("The second argument must be a real number."); } 
/****************************************************************/ 
/* Calltf routine for exp or e**x */ 
exp_call() { tf_putrealp (RETURNV, exp(tf_getrealp(ARG1))); } 
/****************************************************************/ 
/* Calltf routine for natural log */ 
log_call() { tf_putrealp (RETURNV, log(tf_getrealp(ARG1))); } 
/****************************************************************/ 
/* Calltf routine for log base 10 */ 
log10_call() { tf_putrealp (RETURNV, log10(tf_getrealp(ARG1))); } 
/****************************************************************/ 
/* Calltf routine for pow function */ 
pow_call() { tf_putrealp (RETURNV, pow(tf_getrealp(ARG1), tf_getrealp(ARG2))); } 
/****************************************************************/ 
/* Calltf routine for sine function */ 
sin_call() { tf_putrealp (RETURNV, sin(tf_getrealp(ARG1))); } 
/****************************************************************/ 
/* Calltf routine for sqrt function */ 
sqrt_call() { tf_putrealp (RETURNV, sqrt(tf_getrealp(ARG1))); } 

List1: Listing of the C code


$exp   check=math_check1 call=exp_call   size=r 
$log   check=math_check1 call=log_call   size=r 
$log10 check=math_check1 call=log10_call size=r 
$pow   check=math_check2 call=pow_call   size=r 
$sin   check=math_check1 call=sin_call   size=r 
$sqrt  check=math_check1 call=sqrt_call  size=r 
List2 : The math.tab file 




module math;
real x;
initial
   begin
        $display("$exp(2.0) = %f", $exp(2.0));
        $display("$log(44.0) = %f", $log(44.0));
        $display("$log10(100.0) = %f", $log10(100.0));
        $display("$log10(555.0) = %f", $log10(555.0));
        $display("$pow(3.1, 4.1) = %f", $pow(3.1, 4.1));
        $display("$sin(3.14159) = %f", $sin(3.14159));
        $display("$sqrt(169.0) = %f", $sqrt(169.0));
   end
endmodule // math.v

List3 : The sample verilog file using the system call


#!/bin/csh
vcs -R -Mupdate math.v -P math.tab -l vcs.log \
        math.c -CFLAGS "-I$VCS_HOME/`vcs -platform`/lib"

$exp(2.0) = 7.389056
$log(44.0) = 3.784190
$log10(100.0) = 2.000000
$log10(555.0) = 2.744293
$pow(3.1, 4.1) = 103.414859
$sin(3.14159) = 0.000003
$sqrt(169.0) = 13.000000

List4 : Running the simulation

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