Had a go at implementing checked-multiply differently, but the results worked out slower
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@ -114,7 +114,7 @@ static inline int occam_check_retype (int src, int dest, const char *pos) {
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}
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// Some things taken from http://www.fefe.de/intof.html
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#define __HALF_MAX_SIGNED(type) ((type)1 << (sizeof(type)*8-2))
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#define __HALF_MAX_SIGNED(type) ((type)1 << (sizeof(type)*CHAR_BIT-2))
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#define __MAX_SIGNED(type) (__HALF_MAX_SIGNED(type) - 1 + __HALF_MAX_SIGNED(type))
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#define __MIN_SIGNED(type) (-1 - __MAX_SIGNED(type))
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@ -140,9 +140,51 @@ static inline int occam_check_retype (int src, int dest, const char *pos) {
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#define MAKE_SUBTRF(type) \
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static inline type occam_subtr_##type (type, type, const char *) occam_unused; \
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static inline type occam_subtr_##type (type a, type b, const char *pos) { return a - b;}
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#define MAKE_MUL(type) \
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//Here is the plan:
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// - For any values that are smaller than sizeof(long), cast them to long and check that way (TODO).
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// - For all other values, split the number. Take N to be the length of the word
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// and n to be N/2. Split the bits into top(A|B) and bottom(A|B) So we have:
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//A = topA*2^n + bottomA
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//B = topB*2^n + bottomB
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//A*B = (topA*2^n + bottomA) * (topB*2^n + bottomB)
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// = topA*topB*2^N + 2^n*(topA*bottomB + topB*bottomA) + (bottomA*bottomB)
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//
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//If topA*topB is non-zero, the multiplication will definitely overflow. So
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//the multiplication can only be valid if either topA or topB is zero.
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//Then we can see if the middle bracketed multiplication is >= 2^n, in which case
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//the calculation would also overflow. Also, given that either topA or topB is zero,
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//only one of the components of the bracketed sum is non-zero. Finally we do an occam add-style addition
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//of the middle and end, again checking for overflow.
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#define abs(x) ((x) < 0 ? -x : x)
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/* This is my other attempt at the function, but it turned out slower:
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const utype topA = (utype)abs(a) >> (sizeof(type)*CHAR_BIT/2); \
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const utype topB = (utype)abs(b) >> (sizeof(type)*CHAR_BIT/2); \
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const utype bottomA = (utype)abs(a) & (((utype)1<<(sizeof(type)*CHAR_BIT/2))-1); \
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const utype bottomB = (utype)abs(b) & (((utype)1<<(sizeof(type)*CHAR_BIT/2))-1); \
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const utype pos_res = ((a > 0 && b > 0) || (a < 0 && b < 0)) ? 1 : 0; \
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if (topA != 0 && topB != 0) { \
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occam_stop(pos,3,"integer overflow when doing %d * %d", a, b); \
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} else { \
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const utype mid = topA != 0 ? topA*bottomB : topB*bottomA; \
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const utype mid_shift = mid << (sizeof(type)*CHAR_BIT/2); \
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const utype low = bottomA*bottomB; \
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if ((mid>>((utype)1<<(sizeof(type)*CHAR_BIT/2))==0)&&(((utype)__MAX(type))+1-pos_res-mid_shift>=low)) {\
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return (pos_res == 1 ? (type)(mid_shift+low) : -(type)mid_shift-(type)low); \
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} else { \
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occam_stop(pos,3,"integer overflow when doing %d * %d", a, b); \
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} \
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} \
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}
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*/
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#define MAKE_MUL(type,utype) \
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static inline type occam_mul_##type (type, type, const char *) occam_unused; \
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static inline type occam_mul_##type (type a, type b, const char *pos) { \
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static inline type occam_mul_##type (const type a, const type b, const char *pos) { \
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if (( (a < 0 ? -a : a) >> ((sizeof(type)*CHAR_BIT/2)-1) \
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| (b < 0 ? -b : b) >> ((sizeof(type)*CHAR_BIT/2)-1)) == 0) { \
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/*overflow not possible on such small numbers*/ \
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@ -260,7 +302,7 @@ static inline int occam_check_retype (int src, int dest, const char *pos) {
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MAKE_RANGE_CHECK(type,flag) \
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MAKE_ADD(type) \
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MAKE_SUBTR(type) \
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MAKE_MUL(type) \
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MAKE_MUL(type,utype) \
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MAKE_DIV(type) \
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MAKE_REM(type) \
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MAKE_NEGATE(type) \
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@ -273,7 +315,7 @@ static inline int occam_check_retype (int src, int dest, const char *pos) {
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MAKE_RANGE_CHECK(uint8_t, "%d")
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MAKE_ADD(uint8_t)
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MAKE_SUBTR(uint8_t)
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MAKE_MUL(uint8_t)
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MAKE_MUL(uint8_t,uint8_t)
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MAKE_DIV(uint8_t)
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MAKE_SHIFT(uint8_t,uint8_t)
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MAKE_PLUS(uint8_t)
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