Operations on 64-bit operands in 32-bit architectures?

Question

How do most compilers implement operations on 64-bit operands (for example, long int) in 32-bit environments? in other words, is there a way to implement these operations in one step, or do we need to access several memory cells to implement these operations?

Answer 1

They use two registers to store a 64-bit value. One for the lower 32-bit and one for the upper 32-bit.

For x86, 64-bit addition / subtraction is done using the add-with-carry and subtract-with-loan commands:

add   %eax, (lower 32-bits of operand)
adc   %edx, (upper 32-bits of operand)

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