On 4/28/2013 5:18 PM, Dmitriy Gorbel wrote:
Hello, community!
I propose extending the Boost Libraries to provide binary fixed-point arithmetic, within GSOC project.
Fixed-point library will provide nonnegative and negatable class templates for fractional arithmetic, and cardinal and integral for integer arithmetic. In total, four class templates.
Fixed-point arithmetic use more than one notation, and I want to provide several notation to make happy all.
Now I plan to implement two notations - Q notation and notation from C++1y proposal. Examples:
C++1y proposal notation: cardinal<16> 0 <= n < 65536 integral<4> -16 < n < 16 nonnegative<8,-4> 0 <= n < 256 in increments of 2^-4 = 1/16 negatable<16,-8> -65536 < n < 65536 in increments of 2^-8 = 1/256
Q notation: cardinal<16> 0 <= n < 65536 integral<4> -16 < n < 16 nonnegative<8, 4> 0 <= n < 256 has 4 bit for fractional part negatable<16, 8> -65536 < n < 65536 has 8 bit for fractional part
Please, help me to choose default notation, propose other notation, or just make any feedback.
I dislike the names. I don't really understand what the first 2 types have to do with fixed-point math, other than maybe as an implementation detail or degenerate fixed-point type (0 fractional bits). As i understand it: cardinal = fixed-width unsigned int integral = fixed-width signed int nonnegative = cardinal with radix point negatable = integral with radix point At least for Q notation which expects normal 2s complement binary numbers under the hood I still think the ranges are incorrect. The range on negatable<16, 8> should be (in binary) [ 1<<(16+8-1), ~(1<<(16+8-1)) ] convert to real by dividing by (1<<8) gives [ -32768, 32,767.99609375 ] The range on nonnegative<8,4> should be (in binary) [ 0, (1<<(8+4))-1 ] convert to real by dividing by (1<<4) gives [ 0, 255.9375 ]