77 lines
1.5 KiB
V
77 lines
1.5 KiB
V
module math
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pub fn log_n(x f64, b f64) f64 {
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y := log(x)
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z := log(b)
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return y / z
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}
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// log10 returns the decimal logarithm of x.
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// The special cases are the same as for log.
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pub fn log10(x f64) f64 {
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return log(x) * (1.0 / ln10)
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}
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// log2 returns the binary logarithm of x.
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// The special cases are the same as for log.
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pub fn log2(x f64) f64 {
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frac, exp := frexp(x)
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// Make sure exact powers of two give an exact answer.
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// Don't depend on log(0.5)*(1/ln2)+exp being exactly exp-1.
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if frac == 0.5 {
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return f64(exp - 1)
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}
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return log(frac) * (1.0 / ln2) + f64(exp)
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}
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pub fn log1p(x f64) f64 {
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y := 1.0 + x
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z := y - 1.0
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return log(y) - (z - x) / y // cancels errors with IEEE arithmetic
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}
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// log_b returns the binary exponent of x.
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//
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// special cases are:
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// log_b(±inf) = +inf
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// log_b(0) = -inf
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// log_b(nan) = nan
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pub fn log_b(x f64) f64 {
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if x == 0 {
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return inf(-1)
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}
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if is_inf(x, 0) {
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return inf(1)
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}
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if is_nan(x) {
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return x
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}
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return f64(ilog_b_(x))
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}
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// ilog_b returns the binary exponent of x as an integer.
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//
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// special cases are:
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// ilog_b(±inf) = max_i32
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// ilog_b(0) = min_i32
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// ilog_b(nan) = max_i32
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pub fn ilog_b(x f64) int {
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if x == 0 {
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return min_i32
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}
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if is_nan(x) {
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return max_i32
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}
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if is_inf(x, 0) {
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return max_i32
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}
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return ilog_b_(x)
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}
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// ilog_b returns the binary exponent of x. It assumes x is finite and
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// non-zero.
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fn ilog_b_(x_ f64) int {
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x, exp := normalize(x_)
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return int((f64_bits(x) >> shift) & mask) - bias + exp
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}
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