Square root negative exponent handling

pipelined/srt/sqrttestgen.c

@@ -1,6 +1,6 @@
 /* sqrttestgen.c */
 
-/* Written 19 October 2021 David_Harris@hmc.edu
+/* Written 7/22/2022 by Cedar Turek
 
    This program creates test vectors for mantissa component
    of an IEEE floating point square root. 
@@ -15,6 +15,7 @@
 /* Constants */
 
 #define ENTRIES  17
+#define BIGENT   1000
 #define RANDOM_VECS 500
 
 /* Prototypes */
@@ -34,6 +35,9 @@ void main(void)
 			  1.75, 1.875, 1.99999,
 			  1.1, 1.5, 1.01, 1.001, 1.0001,
 			  2/1.1, 2/1.5, 2/1.25, 2/1.125};
+
+  double bigtest[BIGENT];
+
   double exps[ENTRIES] = {0, 0, 2, 3, 4, 5, 6, 7, 8, 1, 10,
         11, 12, 13, 14, 15, 16};
   int i;
@@ -44,13 +48,14 @@ void main(void)
     exit(1);
   }
 
-  for (i=0; i<ENTRIES; i++) {
+  // Small Test
-    aFrac = mans[i];
+  // for (i=0; i<ENTRIES; i++) {
-    aExp  = exps[i] + bias;
+  //   aFrac = mans[i];
-    rFrac = sqrt(aFrac * pow(2, exps[i]));
+  //   aExp  = exps[i] + bias;
-    rExp  = (int) (log(rFrac)/log(2) + bias);
+  //   rFrac = sqrt(aFrac * pow(2, exps[i]));
-    output(fptr, aExp, aFrac, rExp, rFrac);
+  //   rExp  = (int) (log(rFrac)/log(2) + bias);
-  }
+  //   output(fptr, aExp, aFrac, rExp, rFrac);
+  // }
 
   //                                  WS
   // Test 1: sqrt(1) = 1              0000 0000 0000 00
@@ -67,6 +72,16 @@ void main(void)
   //   output(fptr, a, r);
   // }
 
+  // Big Test
+  for (i=0; i<BIGENT; i++) {
+    bigtest[i] = random_input();
+    aFrac = bigtest[i];
+    aExp  = (i - BIGENT/2) + bias;
+    rFrac = sqrt(aFrac * pow(2, (i - BIGENT/2)));
+    rExp  = (int) (log(rFrac)/log(2) + bias);
+    output(fptr, aExp, aFrac, rExp, rFrac);
+  }
+
   fclose(fptr);
 }
 
@@ -105,6 +120,6 @@ void printhex(FILE *fptr, double m)
 
 double random_input(void)
 {
-  return 1.0 + rand()/32767.0;
+  return 1.0 + ((rand() % 32768)/32767.0);
 }
   

pipelined/srt/srt-waves.do

@@ -3,4 +3,5 @@ add wave -noupdate /testbench/srt/*
 add wave -noupdate /testbench/srt/sotfc2/*
 add wave -noupdate /testbench/srt/preproc/*
 add wave -noupdate /testbench/srt/postproc/*
+add wave -noupdate /testbench/srt/expcalc/*
 add wave -noupdate /testbench/srt/divcounter/*

pipelined/srt/srt.sv

@@ -389,11 +389,11 @@ module expcalc(
   input  logic           Sqrt,
   output logic [`NE-1:0] calcExp
 );
-  logic        [`NE-1:0] SExp, DExp, SXExp;
+  logic        [`NE+1:0] SExp, DExp, SXExp;
-  assign SXExp = XExp - (`NE)'(`BIAS);
+  assign SXExp = {2'b00, XExp} - (`NE+2)'(`BIAS);
-  assign SExp  = {1'b0, SXExp[`NE-1:1]} + (`NE)'(`BIAS);
+  assign SExp  = (SXExp >> 1) + (`NE+2)'(`BIAS);
-  assign DExp  = XExp - YExp + (`NE)'(`BIAS);
+  assign DExp  = {2'b00, XExp} - {2'b00, YExp} + (`NE+2)'(`BIAS);
-  assign calcExp = Sqrt ? SExp : DExp;
+  assign calcExp = Sqrt ? SExp[`NE-1:0] : DExp[`NE-1:0];
 
 endmodule
 
@@ -462,11 +462,13 @@ module srtpostproc(
   end
   assign floatRes = S[`DIVLEN] ? S[`DIVLEN:1] : S[`DIVLEN-1:0];
   assign intRes = intS[`DIVLEN] ? intS[`DIVLEN:1] : intS[`DIVLEN-1:0];
-  assign shiftRem = (intRem >>> (`DIVLEN - dur + 2));
+  assign shiftRem = (intRem >> (zeroCntD));
-  always_comb 
+  always_comb begin
-    if (Int)      Result = intRes >> (`DIVLEN - dur);
+    if (Int) begin
-    else if (Mod) Result = shiftRem[`DIVLEN-1:0];
+      if (Mod) Result = shiftRem[`DIVLEN-1:0];
-    else          Result = floatRes;
+      else Result = intRes >> (`DIVLEN - dur);
+    end else Result = floatRes;
+  end
   assign calcSign = XSign ^ YSign;
 endmodule
 

pipelined/srt/testbench.sv

@@ -53,7 +53,7 @@ module testbench;
  
   // Test parameters
   parameter MEM_SIZE = 40000;
-  parameter MEM_WIDTH = 64+64+64+64;
+  parameter MEM_WIDTH = 64+64+64;
  
   // Test sizes
   `define memr  63:0 
@@ -70,9 +70,9 @@ module testbench;
   integer testnum, errors;
 
   // Equip Int, Sqrt, or IntMod test
-  assign Int =  1'b1;
+  assign Int =  1'b0;
   assign Mod =  1'b0;
-  assign Sqrt = 1'b0;
+  assign Sqrt = 1'b1;
 
   // Divider
   srt srt(.clk, .Start(req), 
@@ -101,7 +101,7 @@ module testbench;
     begin
       testnum = 0; 
       errors = 0;
-      $readmemh ("inttestvectors", Tests);
+      $readmemh ("sqrttestvectors", Tests);
       Vec = Tests[testnum];
       a = Vec[`mema];
       {asign, aExp, afrac} = a;