85 lines
1.8 KiB
Zig
85 lines
1.8 KiB
Zig
const math = @import("index.zig");
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const assert = @import("../debug.zig").assert;
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pub fn scalbn(x: var, n: i32) -> @typeOf(x) {
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const T = @typeOf(x);
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switch (T) {
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f32 => @inlineCall(scalbn32, x, n),
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f64 => @inlineCall(scalbn64, x, n),
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else => @compileError("scalbn not implemented for " ++ @typeName(T)),
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}
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}
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fn scalbn32(x: f32, n_: i32) -> f32 {
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var y = x;
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var n = n_;
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if (n > 127) {
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y *= 0x1.0p127;
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n -= 127;
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if (n > 1023) {
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y *= 0x1.0p127;
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n -= 127;
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if (n > 127) {
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n = 127;
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}
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}
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} else if (n < -126) {
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y *= 0x1.0p-126 * 0x1.0p24;
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n += 126 - 24;
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if (n < -126) {
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y *= 0x1.0p-126 * 0x1.0p24;
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n += 126 - 24;
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if (n < -126) {
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n = -126;
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}
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}
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}
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const u = u32(n +% 0x7F) << 23;
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y * @bitCast(f32, u)
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}
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fn scalbn64(x: f64, n_: i32) -> f64 {
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var y = x;
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var n = n_;
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if (n > 1023) {
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y *= 0x1.0p1023;
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n -= 1023;
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if (n > 1023) {
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y *= 0x1.0p1023;
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n -= 1023;
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if (n > 1023) {
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n = 1023;
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}
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}
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} else if (n < -1022) {
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y *= 0x1.0p-1022 * 0x1.0p53;
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n += 1022 - 53;
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if (n < -1022) {
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y *= 0x1.0p-1022 * 0x1.0p53;
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n += 1022 - 53;
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if (n < -1022) {
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n = -1022;
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}
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}
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}
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const u = u64(n +% 0x3FF) << 52;
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y * @bitCast(f64, u)
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}
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test "math.scalbn" {
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assert(scalbn(f32(1.5), 4) == scalbn32(1.5, 4));
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assert(scalbn(f64(1.5), 4) == scalbn64(1.5, 4));
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}
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test "math.scalbn32" {
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assert(scalbn32(1.5, 4) == 24.0);
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}
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test "math.scalbn64" {
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assert(scalbn64(1.5, 4) == 24.0);
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}
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