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Try some ideas to optimize MT19937.

This commit is contained in:
Joris van Rantwijk 2016-10-30 16:18:57 +01:00
parent 6aac5c6356
commit 369da67b11
1 changed files with 28 additions and 19 deletions
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41
rtl/rng_mt19937.vhdl
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@ -113,6 +113,8 @@ architecture rng_mt19937_arch of rng_mt19937 is
signal reg_reseed_cnt: std_logic_vector(9 downto 0);
signal reg_output_buf: std_logic_vector(31 downto 0);
signal reg_seed_a: std_logic_vector(31 downto 0);
signal reg_seed_a2: std_logic_vector(31 downto 0);
signal reg_seed_a3: std_logic_vector(31 downto 0);
signal reg_seed_b: std_logic_vector(31 downto 0);
-- Output register.
@ -125,24 +127,8 @@ architecture rng_mt19937_arch of rng_mt19937 is
is
variable t: unsigned(2*x'length-1 downto 0);
begin
if force_const_mul then
-- Force multiplication via repeated shifts and adds.
return x
+ shift_left(x, 2)
+ shift_left(x, 5)
+ shift_left(x, 6)
+ shift_left(x, 8)
+ shift_left(x, 11)
- shift_left(x, 15)
+ shift_left(x, 19)
- shift_left(x, 26)
- shift_left(x, 28)
+ shift_left(x, 31);
else
-- Let synthesizer choose a multiplier implementation.
t := x * const_f;
return t(x'length-1 downto 0);
end if;
end function;
begin
@ -210,10 +196,33 @@ begin
y := reg_a_wdata;
y(1 downto 0) := y(1 downto 0) xor y(31 downto 30);
reg_seed_a <= y;
if force_const_mul then
-- Multiply by 37.
reg_seed_a2 <= std_logic_vector(
unsigned(y)
+ shift_left(unsigned(y), 2)
+ shift_left(unsigned(y), 5));
-- Multiply by (2**19 - 2**15).
reg_seed_a3 <= std_logic_vector(
shift_left(unsigned(y), 19)
- shift_left(unsigned(y), 15));
end if;
end if;
-- Reseed state 2: Multiply by constant.
if force_const_mul then
-- Finalize multiplication by 1812433253 =
-- (37 + 2**6*37 - 2**15 + 2**19 - 2**26*37)
reg_seed_b <= std_logic_vector(
unsigned(reg_seed_a2)
+ shift_left(unsigned(reg_seed_a2), 6)
+ unsigned(reg_seed_a3)
- shift_left(unsigned(reg_seed_a2), 26));
else
-- Multiply by 1812433253.
-- Let synthesizer choose the multiplier implementation.
reg_seed_b <= std_logic_vector(mulconst(unsigned(reg_seed_a)));
end if;
-- Update internal RNG state.
if reg_enable = '1' then