From 17163cf43a6b6eec9aac44f6a4463dda54b8ed68 Mon Sep 17 00:00:00 2001 From: Xiretza Date: Wed, 8 Apr 2020 19:30:47 +0200 Subject: Add flooring modulo operator The $div and $mod cells use truncating division semantics (rounding towards 0), as defined by e.g. Verilog. Another rounding mode, flooring (rounding towards negative infinity), can be used in e.g. VHDL. The new $modfloor cell provides this flooring modulo (also known as "remainder" in several languages, but this name is ambiguous). This commit also fixes the handling of $mod in opt_expr, which was previously optimized as if it was $modfloor. --- techlibs/common/simlib.v | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) (limited to 'techlibs/common/simlib.v') diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v index 2cdddeabb..57fc07caa 100644 --- a/techlibs/common/simlib.v +++ b/techlibs/common/simlib.v @@ -1021,6 +1021,14 @@ endmodule // -------------------------------------------------------- +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $mod (A, B, Y) +//- +//- Modulo/remainder of division with truncated result (rounded towards 0). +//- +//- Invariant: $div(A, B) * B + $mod(A, B) == A +//- module \$mod (A, B, Y); parameter A_SIGNED = 0; @@ -1043,6 +1051,46 @@ endgenerate endmodule +// -------------------------------------------------------- + +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $modfloor (A, B, Y) +//- +//- Modulo/remainder of division with floored result (rounded towards negative infinity). +//- +//- Invariant: $divfloor(A, B) * B + $modfloor(A, B) == A +//- +module \$modfloor (A, B, Y); + +parameter A_SIGNED = 0; +parameter B_SIGNED = 0; +parameter A_WIDTH = 0; +parameter B_WIDTH = 0; +parameter Y_WIDTH = 0; + +input [A_WIDTH-1:0] A; +input [B_WIDTH-1:0] B; +output [Y_WIDTH-1:0] Y; + +generate + if (A_SIGNED && B_SIGNED) begin:BLOCK1 + localparam WIDTH = B_WIDTH >= Y_WIDTH ? B_WIDTH : Y_WIDTH; + wire [WIDTH-1:0] B_buf, Y_trunc; + assign B_buf = $signed(B); + assign Y_trunc = $signed(A) % $signed(B); + // flooring mod is the same as truncating mod for positive division results (A and B have + // the same sign), as well as when there's no remainder. + // For all other cases, they behave as `floor - trunc = B` + assign Y = (A[A_WIDTH-1] == B[B_WIDTH-1]) || Y_trunc == 0 ? Y_trunc : $signed(B_buf) + $signed(Y_trunc); + end else begin:BLOCK2 + // no difference between truncating and flooring for unsigned + assign Y = A % B; + end +endgenerate + +endmodule + // -------------------------------------------------------- `ifndef SIMLIB_NOPOW -- cgit v1.2.3 From edd8ff2c0778d97808869488cc7394151456c4ca Mon Sep 17 00:00:00 2001 From: Xiretza Date: Tue, 21 Apr 2020 12:51:58 +0200 Subject: Add flooring division operator The $div and $mod cells use truncating division semantics (rounding towards 0), as defined by e.g. Verilog. Another rounding mode, flooring (rounding towards negative infinity), can be used in e.g. VHDL. The new $divfloor cell provides this flooring division. This commit also fixes the handling of $div in opt_expr, which was previously optimized as if it was $divfloor. --- techlibs/common/simlib.v | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) (limited to 'techlibs/common/simlib.v') diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v index 57fc07caa..125b8e013 100644 --- a/techlibs/common/simlib.v +++ b/techlibs/common/simlib.v @@ -997,6 +997,12 @@ endmodule // -------------------------------------------------------- +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $div (A, B, Y) +//- +//- Division with truncated result (rounded towards 0). +//- module \$div (A, B, Y); parameter A_SIGNED = 0; @@ -1053,6 +1059,43 @@ endmodule // -------------------------------------------------------- +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $divfloor (A, B, Y) +//- +//- Division with floored result (rounded towards negative infinity). +//- +module \$divfloor (A, B, Y); + +parameter A_SIGNED = 0; +parameter B_SIGNED = 0; +parameter A_WIDTH = 0; +parameter B_WIDTH = 0; +parameter Y_WIDTH = 0; + +input [A_WIDTH-1:0] A; +input [B_WIDTH-1:0] B; +output [Y_WIDTH-1:0] Y; + +generate + if (A_SIGNED && B_SIGNED) begin:BLOCK1 + localparam WIDTH = + A_WIDTH >= B_WIDTH && A_WIDTH >= Y_WIDTH ? A_WIDTH : + B_WIDTH >= A_WIDTH && B_WIDTH >= Y_WIDTH ? B_WIDTH : Y_WIDTH; + wire [WIDTH:0] A_buf, B_buf, N_buf; + assign A_buf = $signed(A); + assign B_buf = $signed(B); + assign N_buf = (A[A_WIDTH-1] == B[B_WIDTH-1]) || A == 0 ? A_buf : $signed(A_buf - (B[B_WIDTH-1] ? B_buf+1 : B_buf-1)); + assign Y = $signed(N_buf) / $signed(B_buf); + end else begin:BLOCK2 + assign Y = A / B; + end +endgenerate + +endmodule + +// -------------------------------------------------------- + // |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| //- //- $modfloor (A, B, Y) -- cgit v1.2.3