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Chapter 15: Expressions and The Expression Stack
TI
-
89 / TI
-
92 Plus Developer Guide
Not for Distribution
Beta Version January 26, 2001
15.6.1. Estack Arguments and Results
Lets modify the future value function to accept its arguments as a tail on the
estack and return its result on the estack. This example continues to accept and
return only floating-point values. The changes use the following features.
•
An EstackIndex called arg is used to access each of the arguments in turn.
•
BCD16 variables fv, pv, ir, and np are declared to receive the argument
values and perform the computation.
•
The system function
next_expression_index
is used to step from each
argument to the next.
•
The system function
estack_to_float
is used to copy the tagged floats from
the estack into the BCD16 variables.
•
The system function
push_Float
is used to push the BCD16 result onto the
estack as a tagged float.
/* This function takes three tagged BCD16 arguments.
The arguments are required to be in a tail on top
of the expression stack in the following order.
pv = present value
ir = interest rate
np = number of periods
The function returns future value fv as a tagged
float on top of the expression stack.
*/
void fv (void)
{ EStackIndex arg; /* argument pointer */
BCD16 fv, pv, ir, np; /* BCD16 variables */
/* point arg to the first argument in the tail */
arg = top_estack;
/* get the present value argument */
pv = estack_to_float (arg);
/* advance the argument pointer to the next argument */
arg = next_expression_index (arg);
/* get the interest rate argument */
ir = estack_to_float (arg);
/* advance the argument pointer to the next argument */
arg = next_expression_index (arg);
/* get the number of periods argument */
np = estack_to_float (arg);
/* perform the future value calculation */
fv = pv * pow (ir + 1.0, np);
/* push the future value on the estack */
push_Float (fv);
}
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