decode WIP

reimplement/set.py

@@ -45,6 +45,22 @@ def int_to_char(value: int) -> str:
         raise ValueError("Value must be in the range [0, 63] for base64 encoding.")
 
 
+def char_to_int(char: str) -> int:
+    """Convert a base64 character to its corresponding integer value."""
+    if "0" <= char <= "9":
+        return ord(char) - ord("0")
+    elif "a" <= char <= "z":
+        return ord(char) - ord("a") + 10
+    elif "A" <= char <= "Z":
+        return ord(char) - ord("A") + 36
+    elif char == "+":
+        return 62
+    elif char == "/":
+        return 63
+    else:
+        raise ValueError("Character must be a valid base64 character.")
+
+
 def encode_golomb_Mshift(cnt: int, bpp: int) -> int:
     """Calculate Mshift paramter for encoding."""
     Mshift = bpp - (cnt.bit_length() - 1) - 1
@@ -122,10 +138,117 @@ def encode_set(hash_values: List[int], bpp: int) -> str:
     return int_to_char(bpp) + int_to_char(Mshift) + base64_chars
 
 
-def rpmsetcmp():
+def decode_base64(encoded_str: str) -> List[int]:
+    """Decode a base64 string into a list of bits."""
+    bits = []
+
+    for char in encoded_str:
+        value = char_to_int(char)
+        for i in range(6):
+            bits.append((value >> (5 - i)) & 1)
+
+    return bits
+
+
+def decode_golomb(bits: List[int], Mshift: int) -> List[int]:
+    """Decode a list of bits encoded with Golomb coding into delta values."""
+    delta_values = []
+    i = 0
+
+    while i < len(bits):
+        q = 0
+
+        while i < len(bits) and bits[i] == 0:
+            q += 1
+            i += 1
+
+        if i >= len(bits):
+            if q > 5:
+                raise ValueError("Invalid Golomb encoding: too many leading zeros.")
+            break
+
+        i += 1  # skip the separator bit
+
+        r = 0
+        for j in range(Mshift):
+            if i < len(bits):
+                if bits[i] == 1:
+                    r |= 1 << j
+            else:
+                i += 1
+
+        delta_value = (q << Mshift) | r
+        delta_values.append(delta_value)
+
+    return delta_values
+
+
+def decode_delta(delta_values: List[int]) -> List[int]:
+    """Decode a list of delta values into hash values."""
+    last_hash = delta_values[0]
+    hash_values = [last_hash]
+
+    for i in range(1, len(delta_values)):
+        hash_values.append(hash_values[i - 1] + delta_values[i])
+
+    return hash_values
+
+
+def downsample_set(hash_values: List[int], bpp: int) -> List[int]:
+    """Reduce a set of (bpp + 1) values to a set of bpp values, keeping it sorted."""
+    # WIP
     pass
 
 
+def decode_set_init(encoded_str: str) -> Tuple[int, int]:
+    """Decode the initial part of the set-string to extract bpp and Mshift."""
+    if len(encoded_str) < 2:
+        raise ValueError("Encoded string is too short to contain bpp and Mshift.")
+
+    bpp = char_to_int(encoded_str[0])
+    Mshift = char_to_int(encoded_str[1])
+
+    assert check_bpp(bpp), "bpp must be between 2 and 64"
+    assert check_Mshift(Mshift), "Mshift must be between 1 and 63"
+
+    return bpp, Mshift
+
+
+def decode_set(encoded_str: str, Mshift: int) -> List[int]:
+    """Decode the set-string representation into a list of hash values."""
+    data_str = encoded_str[2:]
+
+    str_bits = decode_base64(data_str)
+    str_delta = decode_golomb(str_bits, Mshift)
+    hash_values = decode_delta(str_delta)
+
+    return hash_values
+
+
+def rpmsetcmp(str1: str, str2: str) -> int:
+    if str1[:3] == "set:":
+        str1 = str1[3:]
+    if str2[:3] == "set:":
+        str2 = str2[3:]
+
+    bpp1, Mshift1 = decode_set_init(str1)
+    bpp2, Mshift2 = decode_set_init(str2)
+    hash_values1 = decode_set(str1, Mshift1)
+    hash_values2 = decode_set(str2, Mshift2)
+
+    while bpp1 > bpp2:
+        hash_values1 = downsample_set(hash_values1, bpp1)
+        bpp1 -= 1
+
+    while bpp2 > bpp1:
+        hash_values2 = downsample_set(hash_values2, bpp2)
+        bpp2 -= 1
+
+    # WIP
+
+    return 0
+
+
 def set_new() -> Set:
     """Create a new Set instance with cnt initialized to 0 and an empty list of labels."""
     return Set(cnt=0, labels=[])
@@ -190,3 +313,18 @@ if __name__ == "__main__":
     result = set_fini(my_set, 8)
     print(result)
     set_free(my_set)
+
+    # example with comparison
+    set1 = set_new()
+    set_add(set1, "label1")
+    set_add(set1, "label2")
+    str1 = set_fini(set1, 8)
+    set2 = set_new()
+    set_add(set2, "label1")
+    set_add(set2, "label2")
+    set_add(set2, "label3")
+    str2 = set_fini(set2, 8)
+    assert str1 is not None and str2 is not None, "Set strings should not be None"
+    comparison_result = rpmsetcmp(str1, str2)
+    assert comparison_result == -1, "Expected str1 to be less than str2"
+    print(comparison_result)