What is data[10+:4] data[10-:4]

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I don't understand it.

It may help it you told where it came from.

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I'm find:

http://support.aldec.com/knowledgebase/article.aspx?aid=000786&show=vsa00219.htm

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Indexed part-selects are supported. For vectors where the msb is less than the lsb (e.g. [0:15]) the following syntax is used:

little_vec [msb_base_expr +: width_expr]

This selects the width_expr number of bits starting from bit msb_base_expr. The bit range is ascending. The [2 +: 3] part-select selects bits [2:4] (i.e. three bits starting from bit 2).

For vectors where the msb is greater than the lsb (e.g. [15:0]) the following syntax is used:

big_vec [msb_base_expr -: width_expr]

This selects the width_expr number of bits starting from bit msb_base_expr. The bit range is descending. The [4 -: 3] part-select selects bits [4:2] (i.e. three bits starting from bit 4).

Expressions used in indexed part-selects must be constant expressions. This is a limitation of the current version of the simulator. LRM allows that the msb_base_exp and the lsb_base_exp vary at run time.

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