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C166 User's Guide
C166 Introduction Compiling Programs 
Language Extensions 
Keywords Memory Models Tiny Model Small Model Medium Model Compact Model Large Model HCompact Model HLarge Model XLarge Model Memory Types near far bdata ebdata idata sdata huge xhuge Memory Type Comparison Pointers with Memory Types Implicit Memory Types Type Qualifiers const volatile Data Types Special Function Registers sfr Types sbit Types bit Types Bit-Addressable Objects Function Declarations Return Values Register Bank Register Mask Interrupt Functions Fast Interrupts Cached Vectors Fast Register Banks Inline Functions Real-Time Function Tasks Inline Assembly Traditional Inline Assembly Extended Inline Assembly Operands Operators Register Use Use in Macro Definitions Preprocessor Advanced Programming Error Messages Library Reference AppendixReturn Values
C functions (which are declared as follows) may return a single value with a specified type.
<[>type<]> funcname (<[>args<]>)
where:
| type | is the type of the value returned from the function. If no type is specified, int is assumed. |
| funcname | is the name of the function. |
| args | is the argument list for the function. |
Return values are always returned in registers depending on the return value type. The following table lists return types and the registers used for each.
| Return Type | Register(s) | Description |
|---|---|---|
| bit | R4.0 | |
| signed char unsigned char | RL4 | |
| signed int unsigned int | R4 | |
| signed long unsigned long | R4-R5 | LSB in R4, MSB in R5. |
| float | R4-R5 | 32-bit IEEE format, exponent and sign in R5. |
| double | R4-R7 | 64-bit IEEE format, exponent and sign in R7. |
| near (2-byte) pointer | R4 | |
| far (4-byte) pointer huge (4-byte) pointer | R4-R5 | Offset in R4, selector in R5. |
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