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CARM User's Guide
CARM Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Basic I/O Memory Allocation Interfacing C to Assembler Function Parameters Function Return Values Using the SRC Directive Register Usage Example Routines ARM Code Example Thumb Code Example Data Storage Formats Byte Order Byte Alignment Integer Scalars 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars 8-Byte Scalars float Scalars float Format float Errors double Scalars double Format double Errors Pointers Bit Fields Absolute Memory Access The __at Keyword Linker Location Controls Error Messages Library Reference AppendixFunction Return Values
Function return values are always passed using CPU registers. The following table lists the possible return values and the registers used for each.
| Return Type | Bits | Register | Description |
|---|---|---|---|
| signed char | 8 | R0 | Value returned in the low byte of R0. |
| unsigned char | 8 | R0 | Value returned in the low byte of R0. |
| signed short | 16 | R0 | Value returned in the low half-word of R0. |
| unsigned short | 16 | R0 | Value returned in the low half-word of R0. |
| signed int | 32 | R0 | Value returned in R0. |
| unsigned int | 32 | R0 | Value returned in R0. |
| signed long | 32 | R0 | Value returned in R0. |
| unsigned long | 32 | R0 | Value returned in R0. |
| float | 32 | R0 | Value returned in R0. |
| pointer | 32 | R0 | Value returned in R0. |
| signed long long | 64 | R0-R1 | Low word returned in R0. High word returned in R1. |
| unsigned long long | 64 | R0-R1 | Low word returned in R0. High word returned in R1. |
| double | 64 | R0-R1 | Low word returned in R0. High word returned in R1. |
| struct | R0-R3 | Structs with a total size less than 16 bytes are returned in R0-R3. |
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