Compress the LUT

Author: nielsdos

ext/bcmath/libbcmath/src/recmul.c

@@ -159,17 +159,17 @@ static inline void bc_fast_mul(bc_num n1, size_t n1len, bc_num n2, size_t n2len,
 }
 
 #if BC_LITTLE_ENDIAN
-# define BC_ENCODE_LUT(A, B) ((A) | (B) << 8)
+# define BC_ENCODE_LUT(A, B) ((A) | (B) << 4)
 #else
-# define BC_ENCODE_LUT(A, B) ((B) | (A) << 8)
+# define BC_ENCODE_LUT(A, B) ((B) | (A) << 4)
 #endif
 
 #define LUT_ITERATE(_, A) \
 	_(A, 0), _(A, 1), _(A, 2), _(A, 3), _(A, 4), _(A, 5), _(A, 6), _(A, 7), _(A, 8), _(A, 9)
 
 /* This LUT encodes the decimal representation of numbers 0-100
  * such that we can avoid taking modulos and divisions which would be slow. */
-static const unsigned short LUT[100] = {
+static const unsigned char LUT[100] = {
 	LUT_ITERATE(BC_ENCODE_LUT, 0),
 	LUT_ITERATE(BC_ENCODE_LUT, 1),
 	LUT_ITERATE(BC_ENCODE_LUT, 2),
@@ -182,6 +182,11 @@ static const unsigned short LUT[100] = {
 	LUT_ITERATE(BC_ENCODE_LUT, 9),
 };
 
+static inline unsigned short bc_expand_lut(unsigned char c)
+{
+	return (c & 0x0f) | (c & 0xf0) << 4;
+}
+
 /* Writes the character representation of the number encoded in value.
  * E.g. if value = 1234, then the string "1234" will be written to str. */
 static void bc_write_bcd_representation(uint32_t value, char *str)
@@ -191,10 +196,10 @@ static void bc_write_bcd_representation(uint32_t value, char *str)
 
 #if BC_LITTLE_ENDIAN
 	/* Note: little endian, so `lower` comes before `upper`! */
-	uint32_t digits = LUT[lower] << 16 | LUT[upper];
+	uint32_t digits = bc_expand_lut(LUT[lower]) << 16 | bc_expand_lut(LUT[upper]);
 #else
 	/* Note: big endian, so `upper` comes before `lower`! */
-	uint32_t digits = LUT[upper] << 16 | LUT[lower];
+	uint32_t digits = bc_expand_lut(LUT[upper]) << 16 | bc_expand_lut(LUT[lower]);
 #endif
 	memcpy(str, &digits, sizeof(digits));
 }