C51: STACK REQUIREMENTS OF RUN-TIME LIBRARY FUNCTIONS

Information in this article applies to:

C51 Version 7 or higher

QUESTION

Is there any information about the stack requirements of the Keil C51 run-time library available? I need figures for the floating point arithmetic functions.

ANSWER

Most of the C51 run-time library functions are pretty small and do not require (except for the CALL itself) additional stack space.

No additional stack is required by the following run-time library functions:

Standard Load and Store routines (except when using the far memory type).
unsigned int and unsigned long arithmetic library functions.
signed int and signed long arithmetic library functions, except division.

One additional CALL level (2 or 3 stack bytes) is required by the following run-time library functions:

Auto increment/decrement Load and Store routines, except float.
signed int and signed long division.
unsigned int and unsigned long arithmetic library functions.
floating point add, sub, mul, div and compare.

Two additional CALL levels (4 or 6 stack bytes) are required by the following run-time library functions:

Auto increment/decrement Load and Store routines with data type float.
Floating point square root (sqrt).

Three additional CALL levels (6 or 9 stack bytes) are required by the following run-time library functions:

Floating point trigonometric functions (sin, cos, tan, asin, acos, atan).
Floating point logarithm function (log, log10).
Floating point exponential function (exp).

More complex functions may have even higher stack requirements, however none of the library functions require more than 22 bytes (35 for 3-byte CALL/RET frame size).

Floating point trigonometric functions (sin, cos, tan, asin, acos, atan).
Floating point logartihm (log, log10).

C51: STACK REQUIREMENTS OF RUN-TIME LIBRARY FUNCTIONS

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