==== 7.5.108 swap_x ====

Swap top two operand stack words 

Format 

swap_x 

mn 

Forms 

swap_x = 64 (0x40) 

Stack 

..., wordM+N, ..., wordM+1, wordM, ..., word1 -> ..., wordM, ..., word1, wordM+N, ..., wordM+1 

Description 

The unsigned byte mn is used to construct two parameter values. The high nibble, (mn& 0xf0) >> 4, is used as the value m. The low nibble, (mn& 0xf), is used as the value n. Permissible values for both m and n are 1 and 2. 

The top m words on the operand stack are swapped with the n words immediately below. 

The swap_x instruction must not be used unless the ranges of words 1 through m and words m+1 through n each contain either a 16-bit data type, two 16-bit data types, a 32-bit data type, a 16-bit data type and a 32-bit data type (in either order), or two 32-bit data types. 

Notes 

Except for restrictions preserving the integrity of 32-bit data types, the swap_x instruction operates on untyped words, ignoring the types of data they contain. 

If a virtual machine does not support the int data type, the only permissible value for both m and n is 1.