[MLBEDSW-2845] Improve unit test coverage of fp_math

Improved unit test coverage of fp_math.py

Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
Change-Id: I883fd984a1bfa67102826a400380e41a363fc59d

1 files changed, 36 insertions, 13 deletions

diff --git a/ethosu/vela/fp_math.py b/ethosu/vela/fp_math.py
index eaeb84a1..2515b771 100644
--- a/ethosu/vela/fp_math.py
+++ b/ethosu/vela/fp_math.py
@@ -21,29 +21,49 @@
 # point implementation.
 import numpy as np
 
+# Convert floating point to fixed point, default Q5.26
+def from_float(x, integer_bits=5):
+    i32info = np.iinfo(np.int32)
+    fractional_bits = i32info.bits - integer_bits - 1
+    return min(max(round(x * (1 << fractional_bits)), i32info.min), i32info.max)
+
+
+# Convert fixed point to floating point, default Q5.26
+def to_float(x, integer_bits=5):
+    fractional_bits = np.iinfo(np.int32).bits - integer_bits - 1
+    return x / (1 << fractional_bits)
+
 
 def saturating_rounding_mul(a, b):
     assert np.int32(a) == a
     assert np.int32(b) == b
     if a == b and a == np.iinfo(np.int32).min:
         return np.int32(np.iinfo(np.int32).max)
-    ab = np.int64(a) * np.int64(b)
-    nudge = (1 << 30) if ab >= 0 else (1 - (1 << 30))
-    result = np.int32(np.right_shift(ab + nudge, 31))
-    if result < 0:
-        result += 1
-    return result
+    divider = 1 << 31
+    ab = a * b
+    if ab >= 0:
+        nudge = 1 << 30
+        return (ab + nudge) // divider
+    else:
+        nudge = 1 - (1 << 30)
+        ab_plus_nudge = ab + nudge
+        result = ab_plus_nudge // divider
+        # Python uses floor, the reference uses truncation
+        # so we need to compensate for that.
+        if result * divider < ab_plus_nudge:
+            result += 1
+        return result
 
 
 def shift_left(a, offset):
     assert np.int32(a) == a
     assert offset >= 0
-    a_info = np.iinfo(a)
+    i32_info = np.iinfo(np.int32)
     shifted = a * (1 << offset)
-    if shifted < a_info.min:
-        return np.int32(a_info.min)
-    elif shifted > a_info.max:
-        return np.int32(a_info.max)
+    if shifted < i32_info.min:
+        return np.int32(i32_info.min)
+    elif shifted > i32_info.max:
+        return np.int32(i32_info.max)
     else:
         return np.int32(shifted)
 
@@ -62,7 +82,7 @@ def rounding_divide_by_pot(x, exponent):
     return result
 
 
-def saturating_rounding_multiply_by_pot(exponent, x):
+def saturating_rounding_multiply_by_pot(x, exponent):
     assert np.int32(x) == x
     assert np.int32(exponent) == exponent
     threshold = (1 << (np.iinfo(np.int32).bits - 1 - exponent)) - 1
@@ -79,7 +99,10 @@ def rescale(integer_bits_src, integer_bits_dst, x):
     assert np.int32(integer_bits_dst) == integer_bits_dst
     assert np.int32(x) == x
     exponent = integer_bits_src - integer_bits_dst
-    result = saturating_rounding_multiply_by_pot(exponent, x)
+    if exponent < 0:
+        result = rounding_divide_by_pot(x, -exponent)
+    else:
+        result = saturating_rounding_multiply_by_pot(x, exponent)
     return result