Merge pull request rust-lang/libm#2 from japaric/fmodf

implement fmodf

Author: japaric

libm/src/fmodf.rs

@@ -0,0 +1,89 @@
+use core::u32;
+
+use isnanf;
+
+pub fn fmodf(x: f32, y: f32) -> f32 {
+    let mut uxi = x.to_bits();
+    let mut uyi = y.to_bits();
+    let mut ex = (uxi >> 23 & 0xff) as i32;
+    let mut ey = (uyi >> 23 & 0xff) as i32;
+    let sx = uxi & 0x80000000;
+    let mut i;
+
+    if uyi << 1 == 0 || isnanf(y) || ex == 0xff {
+        return (x * y) / (x * y);
+    }
+
+    if uxi << 1 <= uyi << 1 {
+        if uxi << 1 == uyi << 1 {
+            return 0.0 * x;
+        }
+
+        return x;
+    }
+
+    /* normalize x and y */
+    if ex == 0 {
+        i = uxi << 9;
+        while i >> 31 == 0 {
+            ex -= 1;
+            i <<= 1;
+        }
+
+        uxi <<= -ex + 1;
+    } else {
+        uxi &= u32::MAX >> 9;
+        uxi |= 1 << 23;
+    }
+
+    if ey == 0 {
+        i = uyi << 9;
+        while i >> 31 == 0 {
+            ey -= 1;
+            i <<= 1;
+        }
+
+        uyi <<= -ey + 1;
+    } else {
+        uyi &= u32::MAX >> 9;
+        uyi |= 1 << 23;
+    }
+
+    /* x mod y */
+    while ex > ey {
+        i = uxi - uyi;
+        if i >> 31 == 0 {
+            if i == 0 {
+                return 0.0 * x;
+            }
+            uxi = i;
+        }
+        uxi <<= 1;
+
+        ex -= 1;
+    }
+
+    i = uxi - uyi;
+    if i >> 31 == 0 {
+        if i == 0 {
+            return 0.0 * x;
+        }
+        uxi = i;
+    }
+
+    while uxi >> 23 == 0 {
+        uxi <<= 1;
+        ex -= 1;
+    }
+
+    /* scale result up */
+    if ex > 0 {
+        uxi -= 1 << 23;
+        uxi |= (ex as u32) << 23;
+    } else {
+        uxi >>= -ex + 1;
+    }
+    uxi |= sx;
+
+    f32::from_bits(uxi)
+}

libm/src/lib.rs

@@ -2,11 +2,13 @@
 #![no_std]
 
 mod fabsf;
+mod fmodf;
 mod powf;
 mod scalbnf;
 mod sqrtf;
 
 pub use fabsf::fabsf;
+pub use fmodf::fmodf;
 pub use powf::powf;
 pub use scalbnf::scalbnf;
 pub use sqrtf::sqrtf;
@@ -16,3 +18,7 @@ pub use sqrtf::sqrtf;
 pub fn _eqf(a: u32, b: u32) -> bool {
     (a as i32).wrapping_sub(b as i32).abs() <= 1
 }
+
+fn isnanf(x: f32) -> bool {
+    x.to_bits() & 0x7fffffff > 0x7f800000
+}

libm/test-generator/src/main.rs

@@ -225,6 +225,7 @@ f32_f32! {
 
 // With signature `fn(f32, f32) -> f32`
 f32f32_f32! {
+    fmodf,
     powf,
 }