- **VHDL**
(*http://www.velocityreviews.com/forums/f18-vhdl.html*)

- - **Sign extension**
(*http://www.velocityreviews.com/forums/t376513-sign-extension.html*)

Sign extensionHi everybody,
I'd like to know if there is any smart way to extend the sign of std_logic_vector for exemple : data_in : in std_logic_vector(11 downto 0); data_out : out std_logic_vector(13 downto 0); I want to adjust data_in to data_out size, so what i used to do is: data_out <= data_in(11) & data_in(11) & data_in; But for huge different size it's painfull and not really nice. Is there a smarter way to do it?? May be I should do a function with a loop that do it?? Thank you |

Re: Sign extensionkclo4 a écrit :
> Hi everybody, > > I'd like to know if there is any smart way to extend the sign of > std_logic_vector > > for exemple : > > data_in : in std_logic_vector(11 downto 0); > data_out : out std_logic_vector(13 downto 0); > > I want to adjust data_in to data_out size, so what i used to do is: > > data_out <= data_in(11) & data_in(11) & data_in; > > But for huge different size it's painfull and not really nice. > Is there a smarter way to do it?? May be I should do a function with a > loop that do it?? Use ieee.numeric_std package, signed vectors instead of std_logic_vector and resize function. data_out <= resize(data_in, data_out'length); Nicolas |

Re: Sign extensionkclo4 a écrit :
> Hi everybody, > > I'd like to know if there is any smart way to extend the sign of > std_logic_vector > > for exemple : > > data_in : in std_logic_vector(11 downto 0); > data_out : out std_logic_vector(13 downto 0); > > I want to adjust data_in to data_out size, so what i used to do is: > > data_out <= data_in(11) & data_in(11) & data_in; > > But for huge different size it's painfull and not really nice. > Is there a smarter way to do it?? May be I should do a function with a > loop that do it?? > > Thank you You have it for free in the std_logic_arith package: function SXT(ARG: STD_LOGIC_VECTOR; SIZE: INTEGER) return STD_LOGIC_VECTOR; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_SIGNED.ALL; [...] data_out <= SXT(data_in, data_out'LENGTH); You also have the EXT function, which is the simple extension function _without_ sign extension. |

Re: Sign extensionMany users don't recommend using non-ieee packages such as
std_logic_arith, etc. that were developed by synopsys and compiled into the ieee library without ieee permission/standardization. Since they are not standard, their implementation can and does vary between vendors of simulation and synthesis tools. Better to type a little more and use ieee standard packages that are uniform in their implementation across all vendors. If you need to keep data_in and data_out as SLV: data_out <= std_logic_vector(resize(signed(data_in), data_out'length)); Andy OL wrote: > kclo4 a écrit : > > Hi everybody, > > > > I'd like to know if there is any smart way to extend the sign of > > std_logic_vector > > > > for exemple : > > > > data_in : in std_logic_vector(11 downto 0); > > data_out : out std_logic_vector(13 downto 0); > > > > I want to adjust data_in to data_out size, so what i used to do is: > > > > data_out <= data_in(11) & data_in(11) & data_in; > > > > But for huge different size it's painfull and not really nice. > > Is there a smarter way to do it?? May be I should do a function with a > > loop that do it?? > > > > Thank you > > You have it for free in the std_logic_arith package: > function SXT(ARG: STD_LOGIC_VECTOR; SIZE: INTEGER) return STD_LOGIC_VECTOR; > > use IEEE.STD_LOGIC_ARITH.ALL; > use IEEE.STD_LOGIC_SIGNED.ALL; > [...] > data_out <= SXT(data_in, data_out'LENGTH); > > You also have the EXT function, which is the simple extension function > _without_ sign extension. |

Re: Sign extensionOr if you use appropriately constrained subtypes of integer for
data_out and data_in: data_out <= data_in; Andy Nicolas Matringe wrote: > kclo4 a écrit : > > Hi everybody, > > > > I'd like to know if there is any smart way to extend the sign of > > std_logic_vector > > > > for exemple : > > > > data_in : in std_logic_vector(11 downto 0); > > data_out : out std_logic_vector(13 downto 0); > > > > I want to adjust data_in to data_out size, so what i used to do is: > > > > data_out <= data_in(11) & data_in(11) & data_in; > > > > But for huge different size it's painfull and not really nice. > > Is there a smarter way to do it?? May be I should do a function with a > > loop that do it?? > > Use ieee.numeric_std package, signed vectors instead of std_logic_vector > and resize function. > > data_out <= resize(data_in, data_out'length); > > Nicolas |

Re: Sign extensionNicolas Matringe schrieb:
> Use ieee.numeric_std package, signed vectors instead of std_logic_vector > and resize function. > > data_out <= resize(data_in, data_out'length); Respectively with std_ulogic_vector and the desired conversions: -- either data_out<=std_ulogic_vector(resize(unsigned(data_i n), data_out'length)); -- or data_out<=std_ulogic_vector(resize( signed(data_in), data_out'length)); (I only want to point it out that sign extension of std_ulogic_vectors strongly depends on the fact whether signed or unsigned data representation is desired.) Ralf |

Re: Sign extensionThere is no "sign extension" of unsigned representations, since there
is no sign bit. A resize of an unsigned representation to a larger size just appends enough zeroes to fit, whereas sign extension replicates the MSB enough times to fit. The numeric_std.resize() function is overloaded to perform a sign extend operation when called with a signed argument and return value (assuming it is increasing the size of the argument). Andy Ralf Hildebrandt wrote: > Nicolas Matringe schrieb: > > > > Use ieee.numeric_std package, signed vectors instead of std_logic_vector > > and resize function. > > > > data_out <= resize(data_in, data_out'length); > > Respectively with std_ulogic_vector and the desired conversions: > > -- either > data_out<=std_ulogic_vector(resize(unsigned(data_i n), data_out'length)); > -- or > data_out<=std_ulogic_vector(resize( signed(data_in), data_out'length)); > > (I only want to point it out that sign extension of std_ulogic_vectors > strongly depends on the fact whether signed or unsigned data > representation is desired.) > > Ralf |

Re: Sign extensionAndy schrieb:
> There is no "sign extension" of unsigned representations, since there > is no sign bit. A resize of an unsigned representation to a larger size > just appends enough zeroes to fit, whereas sign extension replicates > the MSB enough times to fit. Yes, I know - but I wanted to point out, that nobody can say, what is inside a std_logic_vector: just bits, signed or unsigned data. And even adding zeros while resizing an unsigned vector is some kind of sign extension, because an unsigned vector has always an implicit zero as sign. Ralf |

Re: Sign extensionkclo4 wrote:
> Hi everybody, > > I'd like to know if there is any smart way to extend the sign of > std_logic_vector > > for exemple : > > data_in : in std_logic_vector(11 downto 0); > data_out : out std_logic_vector(13 downto 0); > > I want to adjust data_in to data_out size, so what i used to do is: > > data_out <= data_in(11) & data_in(11) & data_in; > > But for huge different size it's painfull and not really nice. > Is there a smarter way to do it?? May be I should do a function with a > loop that do it?? > > Thank you Don't need any libraries or loops if you do this: data_out(11 downto 0) <= data_in; data_out(13 downto 12) <= (13 downto 12 => data_in(11)); |

Re: Sign extensionRalf Hildebrandt a écrit :
> (I only want to point it out that sign extension of std_ulogic_vectors > strongly depends on the fact whether signed or unsigned data > representation is desired.) I assumed that sign extension was only needed for signed vectors. Nicolas |

All times are GMT. The time now is 10:22 AM. |

Powered by vBulletin®. Copyright ©2000 - 2014, vBulletin Solutions, Inc.

SEO by vBSEO ©2010, Crawlability, Inc.