X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Fadd%2Ffsqrt.py;h=02449b0f75b41b0ba2e004711d9570ccca49ca3d;hb=aa8c754e7d66345a67faa0804e97f38612b283c1;hp=c2d32a7acbbdf4c3e3cb84d0465be4ba52bcc392;hpb=7c76f6c047bfb3110d611e9038bc8fd9a1293a73;p=ieee754fpu.git

diff --git a/src/add/fsqrt.py b/src/add/fsqrt.py
index c2d32a7a..02449b0f 100644
--- a/src/add/fsqrt.py
+++ b/src/add/fsqrt.py
@@ -1,9 +1,13 @@
+from sfpy import Float32
+
+
+# XXX DO NOT USE, fails on num=65536.  wark-wark...
 def sqrtsimple(num):
     res = 0
-    bit = 1 << 14
+    bit = 1
 
-    while (bit > num):
-        bit >>= 2
+    while (bit < num):
+        bit <<= 2
 
     while (bit != 0):
         if (num >= res + bit):
@@ -16,34 +20,27 @@ def sqrtsimple(num):
     return res
 
 
-# XXX DO NOT USE, fails on num=65536.  wark-wark...
 def sqrt(num):
     D = num # D is input (from num)
-    Q = 0
-    R = 0
-    r = 0 # remainder
-    for i in range(15, -1, -1): # negative ranges are weird...
-
-        if (R>=0):
-        
-            R = (R<<2)|((D>>(i+i))&3)
-            R = R-((Q<<2)|1) #/*-Q01*/
-         
-        else:
+    Q = 0 # quotient
+    R = 0 # remainder
+    for i in range(64, -1, -1): # negative ranges are weird...
 
-            R = (R<<2)|((D>>(i+i))&3)
-            R = R+((Q<<2)|3) #/*+Q11*/
-        
-        if (R>=0):
-            Q = (Q<<1)|1 #/*new Q:*/
+        R = (R<<2)|((D>>(i+i))&3)
+
+        if R >= 0:
+            R -= ((Q<<2)|1) # -Q01
         else:
-            Q = (Q<<1)|0 #/*new Q:*/
-    
+            R += ((Q<<2)|3) # +Q11
+
+        Q <<= 1
+        if R >= 0:
+            Q |= 1 # new Q
 
-    if (R<0):
-        R = R+((Q<<1)|1)
-        r = R
-    return Q
+    if R < 0:
+        R = R + ((Q<<1)|1)
+
+    return Q, R
 
 
 # grabbed these from unit_test_single (convenience, this is just experimenting)
@@ -60,24 +57,109 @@ def set_exponent(x, e):
 def get_sign(x):
     return ((x & 0x80000000) >> 31)
 
+# convert FP32 to s/e/m
+def create_fp32(s, e, m):
+    """ receive sign, exponent, mantissa, return FP32 """
+    return set_exponent((s << 31) | get_mantissa(m))
+
+# convert s/e/m to FP32
+def decode_fp32(x):
+    """ receive FP32, return sign, exponent, mantissa """
+    return get_sign(x), get_exponent(x), get_mantissa(x)
+
+
 # main function, takes mantissa and exponent as separate arguments
 # returns a tuple, sqrt'd mantissa, sqrt'd exponent
 
 def main(mantissa, exponent):
     if exponent & 1 != 0:
-        return sqrt(mantissa << 1), # shift mantissa up
-                ((exponent - 1) / 2) # subtract 1 from exp to compensate
-    return sqrt(mantissa),      # mantissa as-is
-           (exponent / 2)       # no compensating needed on exp
+        # shift mantissa up, subtract 1 from exp to compensate
+        mantissa <<= 1
+        exponent -= 1
+    m, r = sqrt(mantissa)
+    return m, r, exponent >> 1
+
+
+#normalization function
+def normalise(s, m, e, lowbits):
+    if (lowbits >= 2):
+        m += 1
+    if get_mantissa(m) == ((1<<24)-1):
+        e += 1
+    return s, m, e
+
 
+def fsqrt_test(x):
+
+    xbits = x.bits
+    print ("x", x, type(x))
+    sq_test = x.sqrt()
+    print ("sqrt", sq_test)
+
+    print (xbits, type(xbits))
+    s, e, m = decode_fp32(xbits)
+    print("x decode", s, e, m, hex(m))
+
+    m |= 1<<23 # set top bit (the missing "1" from mantissa)
+    m <<= 27
+
+    sm, sr, se = main(m, e)
+    lowbits = sm & 0x3
+    sm >>= 2
+    sm = get_mantissa(sm)
+    #sm += 2
+
+    s, sm, se = normalise(s, sm, se, lowbits)
+
+    print("our  sqrt", s, se, sm, hex(sm), bin(sm), "lowbits", lowbits,
+                                                    "rem", hex(sr))
+    if lowbits >= 2:
+        print ("probably needs rounding (+1 on mantissa)")
+
+    sq_xbits = sq_test.bits
+    s, e, m = decode_fp32(sq_xbits)
+    print ("sf32 sqrt", s, e, m, hex(m), bin(m))
+    print ()
 
 if __name__ == '__main__':
-    for Q in range(1, int(1e7)):
+
+    # quick test up to 1000 of two sqrt functions
+    for Q in range(1, int(1e4)):
         print(Q, sqrt(Q), sqrtsimple(Q), int(Q**0.5))
         assert int(Q**0.5) == sqrtsimple(Q), "Q sqrtsimpl fail %d" % Q
-        assert int(Q**0.5) == sqrt(Q), "Q sqrt fail %d" % Q
+        assert int(Q**0.5) == sqrt(Q)[0], "Q sqrt fail %d" % Q
+
+    # quick mantissa/exponent demo
+    for e in range(26):
+        for m in range(26):
+            ms, mr, es = main(m, e)
+            print("m:%d e:%d sqrt: m:%d-%d e:%d" % (m, e, ms, mr, es))
+
+    x = Float32(1234.123456789)
+    fsqrt_test(x)
+    x = Float32(32.1)
+    fsqrt_test(x)
+    x = Float32(16.0)
+    fsqrt_test(x)
+    x = Float32(8.0)
+    fsqrt_test(x)
+    x = Float32(8.5)
+    fsqrt_test(x)
+    x = Float32(3.14159265358979323)
+    fsqrt_test(x)
+    x = Float32(12.99392923123123)
+    fsqrt_test(x)
+    x = Float32(0.123456)
+    fsqrt_test(x)
+
+
+
 
 """
+
+Notes:
+https://pdfs.semanticscholar.org/5060/4e9aff0e37089c4ab9a376c3f35761ffe28b.pdf
+
 //This is the main code of integer sqrt function found here:http://verilogcodes.blogspot.com/2017/11/a-verilog-function-for-finding-square-root.html
 //