ST20-C1 datasheet(185/205 Pages) STMICROELECTRONICS

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1C; B; A

C;A;B;rev

B; C; rev; A

A; C; rev; B; rev

The choice of loading sequence, and of which operands should be evaluated in

advance is determined by the number of registers required to evaluate each of the

operands.

In particular, if

C requires more than two registers it must be loaded before A and B.If

A or B requires more than two registers it must be evaluated before C and may need

to be stored in a temporary variable if

C requires more than two registers.

Table 8.1 gives the instruction sequences needed for loading three operands into the

evaluation stack, where the number in the ‘load sequence’ column refers to the list

above. The columns labelled ‘temp’ indicate where a local variable is needed to

temporarily save an operand value in the load sequence. The variable ‘a’ is used to

store operand ‘A’ and the variable ‘b’ is used to store operand ‘B’.

registers

required

temp

load

sequence

instructions

≤ 2

C; B; A

C; A; B; rev

A; C; rev; B; rev

C; B; A

A; stl a; C; B; ldl a

B; C; rev; A

A; stl a; B; C; rev; ldl a

C; B; A

C; A; B; rev

A; stl a; C; B; ldl a

C; B; A

A; stl a; C; B; ldl a

B; stl b; C; ldl b; A

B; stl b; C; A; ldl b; rev

A; stl a; B; stl b; C; ldl b; ldl a

Table 8.1 Register loading sequences

ST20-C1 Datasheet(PDF) 185 Page - STMicroelectronics