# Debugger Expressions Guide¶

Expressions can be used anywhere a numeric parameter is expected. The syntax for expressions is very close to standard C-style syntax with full operator ordering and parentheses. There are a few operators missing (notably the trinary ? : operator), and a few new ones (memory accessors). The table below lists all the operators in their order, highest precedence operators first.

( ) : standard parentheses
++ -- : postfix increment/decrement
++ -- ~ ! - + b@ w@ d@ q@ : prefix inc/dec, binary NOT, logical NOT, unary +/-, memory access
* / % : multiply, divide, modulus
<< >> : shift left/right
< <= > >= : less than, less than or equal, greater than, greater than or equal
== != : equal, not equal
& : binary AND
^ : binary XOR
| : binary OR
&& : logical AND
|| : logical OR
= *= /= %= += -= <<= >>= &= |= ^= : assignment
, : separate terms, function parameters

## Numbers¶

Numbers are prefixed according to their bases:

• Hexadecimal (base-16) numbers are prefixed with `\$` or `0x`.

• Decimal (base-10) numbers are prefixed with `#`.

• Octal (base-8) numbers are prefixed with `0o`.

• Binary (base-2) numbers are prefixed with `0b`.

• Unprefixed numbers are hexadecimal (base-16).

Examples:

• `123` is 123 hexadecimal (291 decimal).

• `\$123` is 123 hexadecimal (291 decimal).

• `0x123` is 123 hexadecimal (291 decimal).

• `#123` is 123 decimal.

• `0o123` is 123 octal (83 decimal).

• `0b1001` is 9 decimal.

• `0b123` is invalid.

## Differences from C Behaviors¶

• First, all math is performed on full 64-bit unsigned values, so things like a < 0 won't work as expected.

• Second, the logical operators && and || do not have short-circuit properties -- both halves are always evaluated.

• Finally, the new memory operators work like this:

• b!<addr> refers to the byte at <addr> but does NOT suppress side effects such as reading a mailbox clearing the pending flag, or reading a FIFO removing an item.

• b@<addr> refers to the byte at <addr> while suppressing side effects.

• Similarly, w@ and w! refer to a word in memory, d@ and d! refer to a dword in memory, and q@ and q! refer to a qword in memory.

The memory operators can be used as both lvalues and rvalues, so you can write b@100 = ff to store a byte in memory. By default these operators read from the program memory space, but you can override that by prefixing them with a 'd' or an 'i'.

As such, dw@300 refers to data memory word at address 300 and id@400 refers to an I/O memory dword at address 400.