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Startup Code Variable Initialization Code Basic I/O Memory Allocation Optimizer General Optimizations 251-Specific Optimizations Options for Code Generation Global Register Coloring Segment Naming Conventions Segment Types Initialization Segments Function Symbols Parameter Passing Symbols Hardware Stack Calculating Stack Size Interfacing C Programs to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments TINY Model XTINY Model SMALL Model XSMALL Model LARGE Model Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Floating-point Numbers Floating-point Errors Double Numbers Double Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging Error Messages Library Reference AppendixData Storage Formats
This section describes the storage formats of the data types available in the C251 compiler. The C251 compiler offers a number of basic data types to use in your C programs. The following table lists these data types along with their size requirements and value ranges.
| Data Type | Bits | Bytes | Value Range |
|---|---|---|---|
| bit | 1 | — | 0 to 1 |
| signed char | 8 | 1 | -128 to +127 |
| unsigned char | 8 | 1 | 0 to 255 |
| enum | 16 | 2 | -32768 to +32767 |
| signed short | 16 | 2 | -32768 to +32767 |
| unsigned short | 16 | 2 | 0 to 65535 |
| signed int | 16 | 2 | -32768 to +32767 |
| unsigned int | 16 | 2 | 0 to 65535 |
| signed long | 32 | 4 | -2147483648 to 2147483647 |
| unsigned long | 32 | 4 | 0 to 4294967295 |
| float | 32 | 4 | ±1.175494E-38 to ±3.402823E+38 |
| double | 64 | 8 | ±1.7E-308 to ±1.7E+308 |
| data *, idata *, pdata * | 8 | 1 | 0x00 to 0xFF |
| code*, xdata *, near* | 16 | 2 | 0x0000 to 0xFFFF |
| far*, huge* | 32 | 4 | linear 16Mbyte address 0x000000 to 0xFFFFFF |
Other data types, like structures and unions, may contain scalars from this table. All elements of these data types are allocated sequentially and are byte-aligned due to the 8-bit architecture of the 251 family.
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