The assembler interprets all scalar constants as twos-complement numbers. In 32-bit mode, a scalar constant is 32 bits. 64 bits is the size of a scalar constant in 64-bit mode. Scalar constants can be any of the alphanumeric characters 0123456789abcdefABCDEF. You can use an all or LL suffix to identify a 64-bit constant.

Scalar constants can be one of the following:

Floating-point constants can appear only in .float and .double pseudo-operations (directives) (see Chapter 8, “Pseudo Op-Codes (Directives)”), and in the floating-point Load Immediate instructions (see Chapter 6, “Coprocessor Instruction Set”). Floating-point constants have this format:

+d1[.d2][e|E+d3]

where:

For example:

21.73E-3

represents the number .02173.

Optionally, .float and .double directives may use hexadecimal floating-point constants instead of decimal ones. A hexadecimal floating-point constant consists of:

<+ or -> 0x <1 or 0 or nothing> . <hex digits> H 0x <hex digits>

The assembler places the first set of hex digits (excluding the 0 or 1 preceding the decimal point) in the mantissa field of the floating-point format without attempting to normalize it. It stores the second set of hex digits into the exponent field without biasing them. It checks that the exponent is appropriate if the mantissa appears to be denormalizing. Hexadecimal floating-point constants are useful for generating IEEE special symbols, and for writing hardware diagnostics.

For example, either of the following generates a single-precision "1.0":

.float 1.0e+0
.float 0x1.0h0x7f

String constants begin and end with double quotation marks (").

The assembler observes C language backslash conventions. For octal notation, the backslash conventions require three characters when the next character can be confused with the octal number. For hexadecimal notation, the backslash conventions require two characters when the next character can be confused with the hexadecimal number (that is, use a 0 for the first character of a single character hex number).

The assembler follows the backslash conventions shown in Table 4-1.

A label definition consists of an identifier followed by a colon. Label definitions assign the current value and type of the location counter to the name. An error results when the name is already defined, the assigned value changes the label definition, or both conditions exist.

Label definitions always end with a colon. You can put a label definition on a line by itself.

A generated label is a single numeric value (1...255). To reference a generated label, put an f (forward) or a b (backward) immediately after the digit. The reference tells the assembler to look for the nearest generated label that corresponds to the number in the lexically forward or backward direction.

A null statement is an empty statement that the assembler ignores. Null statements can have label definitions. For example, this line has three null statements in it:

label: ; ;

A keyword statement begins with a predefined keyword. The syntax for the rest of the statement depends on the keyword. All instruction opcodes are keywords. All other keywords are assembler pseudo-operations (directives).

Unless parentheses enforce precedence, the assembler evaluates all operators of the same precedence strictly from left to right. Because parentheses also designate index-registers, ambiguity can arise from parentheses in expressions. To resolve this ambiguity, put a unary + in front of parentheses in expressions.

The assembler has three precedence levels, which are listed here from lowest to highest precedence:

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Note: The assembler's precedence scheme differs from that of the C language.

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For expressions, you can rely on the precedence rules, or you can group expressions with parentheses. The assembler recognizes the operators listed in Table 4-2.

The assembler manipulates several types of expressions. Each symbol you reference or define belongs to one of the categories shown in Table 4-3.

Symbols in the undefined and small undefined categories are always global (that is, they are visible to the link editor and can be shared with other modules of your program). Symbols in the absolute, text, data, sdata, rdata, bss, and sbss categories are local unless declared in a .globl pseudo-op.

When expression operators combine expression operands, the result's type depends on the types of the operands and on the operator. Expressions follow these type propagation rules: