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FPU: Decide on mask length a cycle earlier

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This moves longmask into the reg_type record, meaning that it now
needs to be decided a cycle earlier, in order to help timing.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2020-09-01 15:28:19 +10:00
parent fb5115c944
commit e1ca023bad
1 changed files with 8 additions and 5 deletions
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13
fpu.vhdl
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@@ -118,6 +118,7 @@ architecture behaviour of fpu is
use_c : std_ulogic;
invalid : std_ulogic;
negate : std_ulogic;
longmask : std_ulogic;
end record;
type lookup_table is array(0 to 1023) of std_ulogic_vector(17 downto 0);
@@ -615,7 +616,6 @@ begin
variable need_check : std_ulogic;
variable msb : std_ulogic;
variable is_add : std_ulogic;
variable longmask : std_ulogic;
variable set_a : std_ulogic;
variable set_b : std_ulogic;
variable set_c : std_ulogic;
@@ -644,6 +644,7 @@ begin
v.fe_mode := or (e_in.fe_mode);
v.dest_fpr := e_in.frt;
v.single_prec := e_in.single;
v.longmask := e_in.single;
v.int_result := '0';
v.rc := e_in.rc;
v.is_cmp := e_in.out_cr;
@@ -747,7 +748,6 @@ begin
renormalize := '0';
set_x := '0';
qnan_result := '0';
longmask := r.single_prec;
set_a := '0';
set_b := '0';
set_c := '0';
@@ -1204,6 +1204,7 @@ begin
if r.a.exponent = r.b.exponent then
v.state := ADD_2;
else
v.longmask := '0';
v.state := ADD_SHIFT;
end if;
else
@@ -1580,14 +1581,15 @@ begin
-- transferring B to R
v.shift := r.b.exponent - r.a.exponent;
v.result_exp := r.b.exponent;
v.longmask := '0';
v.state := ADD_SHIFT;
when ADD_SHIFT =>
-- r.shift = - exponent difference
-- r.shift = - exponent difference, r.longmask = 0
opsel_r <= RES_SHIFT;
v.x := s_nz;
set_x := '1';
longmask := '0';
v.longmask := r.single_prec;
if r.add_bsmall = '1' then
v.opsel_a := AIN_A;
else
@@ -1676,6 +1678,7 @@ begin
set_s := '1';
f_to_multiply.valid <= r.first;
if multiply_to_f.valid = '1' then
v.longmask := '0';
v.state := ADD_SHIFT;
end if;
@@ -2367,7 +2370,7 @@ begin
-- Data path.
-- This has A and B input multiplexers, an adder, a shifter,
-- count-leading-zeroes logic, and a result mux.
if longmask = '1' then
if r.longmask = '1' then
mshift := r.shift + to_signed(-29, EXP_BITS);
else
mshift := r.shift;