Yes, that would work too.

And it’s standard. And it’s a lot easier to read.

It’s pretty much the same thing.

Yes and no, but mostly no.
The intermediate 16-bit value function di() produces uses a proprietary bit layout. Besides being non-standard and harder to read code, another consequence is that standard arithmetics – like adding, subtracting, multiplying and dividing – do not work on negative numbers. Perhaps there’s still a good reason to use this proprietary format, but it must be a really good one to justify the disadvantages.

Standard negative numbers use two’s complement for negative counter parts of positive integers. This is necessary to keep standard arithmetics intact and hence 0 – 1 = -1. With your proprietary format, you have two zeroes: +0 and -0. And standard arithmetics are broken: +0 – 1 = -32767 and -0 – 1 = 32767

Double:      | Standard conversion (binary)            | Proprietary conversion (binary)| Standard reverse    | Proprietary reverse
-------------+-----------------------------------------+--------------------------------+---------------------+---------------------
value = -2.00, double2fixed = -200 (0b1111111100111000), di = 32968 (0b1000000011001000), fixed2double = -2.00, id = -2.00
value = -1.90, double2fixed = -190 (0b1111111101000010), di = 32958 (0b1000000010111110), fixed2double = -1.90, id = -1.90
value = -1.80, double2fixed = -179 (0b1111111101001101), di = 32947 (0b1000000010110011), fixed2double = -1.79, id = -1.79
value = -1.70, double2fixed = -169 (0b1111111101010111), di = 32937 (0b1000000010101001), fixed2double = -1.69, id = -1.69
value = -1.60, double2fixed = -159 (0b1111111101100001), di = 32927 (0b1000000010011111), fixed2double = -1.59, id = -1.59
value = -1.50, double2fixed = -149 (0b1111111101101011), di = 32917 (0b1000000010010101), fixed2double = -1.49, id = -1.49
value = -1.40, double2fixed = -139 (0b1111111101110101), di = 32907 (0b1000000010001011), fixed2double = -1.39, id = -1.39
value = -1.30, double2fixed = -129 (0b1111111101111111), di = 32897 (0b1000000010000001), fixed2double = -1.29, id = -1.29
value = -1.20, double2fixed = -119 (0b1111111110001001), di = 32887 (0b1000000001110111), fixed2double = -1.19, id = -1.19
value = -1.10, double2fixed = -109 (0b1111111110010011), di = 32877 (0b1000000001101101), fixed2double = -1.09, id = -1.09
value = -1.00, double2fixed =  -99 (0b1111111110011101), di = 32867 (0b1000000001100011), fixed2double = -0.99, id = -0.99
value = -0.90, double2fixed =  -89 (0b1111111110100111), di = 32857 (0b1000000001011001), fixed2double = -0.89, id = -0.89
value = -0.80, double2fixed =  -79 (0b1111111110110001), di = 32847 (0b1000000001001111), fixed2double = -0.79, id = -0.79
value = -0.70, double2fixed =  -69 (0b1111111110111011), di = 32837 (0b1000000001000101), fixed2double = -0.69, id = -0.69
value = -0.60, double2fixed =  -59 (0b1111111111000101), di = 32827 (0b1000000000111011), fixed2double = -0.59, id = -0.59
value = -0.50, double2fixed =  -49 (0b1111111111001111), di = 32817 (0b1000000000110001), fixed2double = -0.49, id = -0.49
value = -0.40, double2fixed =  -39 (0b1111111111011001), di = 32807 (0b1000000000100111), fixed2double = -0.39, id = -0.39
value = -0.30, double2fixed =  -29 (0b1111111111100011), di = 32797 (0b1000000000011101), fixed2double = -0.29, id = -0.29
value = -0.20, double2fixed =  -19 (0b1111111111101101), di = 32787 (0b1000000000010011), fixed2double = -0.19, id = -0.19
value = -0.10, double2fixed =   -9 (0b1111111111110111), di = 32777 (0b1000000000001001), fixed2double = -0.09, id = -0.09
value =  0.00, double2fixed =    0 (0b0000000000000000), di =     0 (0b0000000000000000), fixed2double =  0.00, id =  0.00
value =  0.10, double2fixed =   10 (0b0000000000001010), di =    10 (0b0000000000001010), fixed2double =  0.10, id =  0.10
value =  0.20, double2fixed =   20 (0b0000000000010100), di =    20 (0b0000000000010100), fixed2double =  0.20, id =  0.20
value =  0.30, double2fixed =   30 (0b0000000000011110), di =    30 (0b0000000000011110), fixed2double =  0.30, id =  0.30
value =  0.40, double2fixed =   40 (0b0000000000101000), di =    40 (0b0000000000101000), fixed2double =  0.40, id =  0.40
value =  0.50, double2fixed =   50 (0b0000000000110010), di =    50 (0b0000000000110010), fixed2double =  0.50, id =  0.50
value =  0.60, double2fixed =   60 (0b0000000000111100), di =    60 (0b0000000000111100), fixed2double =  0.60, id =  0.60
value =  0.70, double2fixed =   70 (0b0000000001000110), di =    70 (0b0000000001000110), fixed2double =  0.70, id =  0.70
value =  0.80, double2fixed =   80 (0b0000000001010000), di =    80 (0b0000000001010000), fixed2double =  0.80, id =  0.80
value =  0.90, double2fixed =   90 (0b0000000001011010), di =    90 (0b0000000001011010), fixed2double =  0.90, id =  0.90
value =  1.00, double2fixed =  100 (0b0000000001100100), di =   100 (0b0000000001100100), fixed2double =  1.00, id =  1.00
value =  1.10, double2fixed =  110 (0b0000000001101110), di =   110 (0b0000000001101110), fixed2double =  1.10, id =  1.10
value =  1.20, double2fixed =  120 (0b0000000001111000), di =   120 (0b0000000001111000), fixed2double =  1.20, id =  1.20
value =  1.30, double2fixed =  130 (0b0000000010000010), di =   130 (0b0000000010000010), fixed2double =  1.30, id =  1.30
value =  1.40, double2fixed =  140 (0b0000000010001100), di =   140 (0b0000000010001100), fixed2double =  1.40, id =  1.40
value =  1.50, double2fixed =  150 (0b0000000010010110), di =   150 (0b0000000010010110), fixed2double =  1.50, id =  1.50
value =  1.60, double2fixed =  160 (0b0000000010100000), di =   160 (0b0000000010100000), fixed2double =  1.60, id =  1.60
value =  1.70, double2fixed =  170 (0b0000000010101010), di =   170 (0b0000000010101010), fixed2double =  1.70, id =  1.70
value =  1.80, double2fixed =  180 (0b0000000010110100), di =   180 (0b0000000010110100), fixed2double =  1.80, id =  1.80
value =  1.90, double2fixed =  190 (0b0000000010111110), di =   190 (0b0000000010111110), fixed2double =  1.90, id =  1.90
value =  2.00, double2fixed =  200 (0b0000000011001000), di =   200 (0b0000000011001000), fixed2double =  2.00, id =  2.00