WIP: IEEE754

test/TestIEEE754.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+pragma abicoder v2;
+
+import "forge-std/Test.sol";
+
+library IEEE754 {
+
+    // reduce (signed)) int to p bits
+
+    function bits2int (uint256 b, uint256 p) internal pure returns (int256 r) {
+        require(p >= 1 && p <= 256, "p invalid");
+        uint256 s = 256 - p;
+        r = int256( b << s ) >> s;
+    }
+
+    int32  internal constant EBIAS      = 127;
+    int32  internal constant ENAN       = 0xff; // Also includes infinity
+    int32  internal constant ESUBNORM   = 0;
+
+    uint32 internal constant SIGN_MASK  = 0x8000_0000;
+    uint32 internal constant EXP_MASK   = 0x7f80_0000;
+    uint32 internal constant MANT_MASK  = 0x007f_ffff;
+    uint32 internal constant ZERO_MASK  = EXP_MASK | MANT_MASK;
+    int32  internal constant MSB        = 0x0080_0000;
+
+    // Todo rounding
+
+    function float2fixed(uint32 floatingPoint, uint256 fixedBits) internal pure returns (int256 fixedPoint) {unchecked{
+
+        // Zero case
+
+        if (floatingPoint & ZERO_MASK == 0) return 0;
+
+        // Extract exponent field
+
+        int32  exp = int32(floatingPoint & EXP_MASK) >> 23;
+        require (exp != ENAN, "NaN not supported");
+
+        // Extract mantisa
+    
+        int256 mant = int32(floatingPoint & MANT_MASK);
+        if (exp != ESUBNORM) mant |= MSB;                 // Add implied MSB to non-subnormal
+        if (floatingPoint & SIGN_MASK != 0) mant = -mant; // Negate if sign bit set
+
+        // Compute shift amount
+
+        exp = exp - EBIAS; // Remove exponent bias
+        int256 rshft = 23 - int256(fixedBits) - exp; // Zero exp and integer fixedPoint throws away all but MSB
+
+        // Shift to arrive at fixed point alignment
+
+        if (rshft < 0) // Most likely case?
+            fixedPoint = mant << uint256(-rshft);
+        else if (rshft > 0)
+            fixedPoint = mant >> uint256(rshft);
+        else
+            fixedPoint = mant;
+
+        return fixedPoint;
+    }}
+}
+
+contract TestIEEE754 is Test {
+
+    function setUp() external pure {
+        console2.log('TestFloat setup()');
+    }
+
+    // Useful constants
+
+    uint256 constant internal umin = 0;
+    uint256 constant internal umax = ~umin;           // 0xff...
+    int256  constant internal imax = int256(umax>>1); // 0x7f...
+    int256  constant internal imin = ~imax;           // 0x80...
+
+    // must be external because called as this.sanityReverts
+
+    function sanityReverts(int256 t) external pure {
+        console2.log("sanityReverts", t);
+        uint256 u;
+        int256 i;
+        if (t == 1) {
+            u = umax+1; // Overflow
+        } else if (t == 2) {
+            u = umin-1; // Underflow
+        } else if (t == 3) {
+            i = imax+1; // Overflow
+        } else if (t == 4) {
+            i = imin-1; // Underflow
+        } else {
+            // Will not revert
+        }
+    }
+
+    function testSanity() external {
+        console2.log('Float.testSanity()');
+        int256 i;
+        for (i=1; i<=4; i++) {
+            vm.expectRevert();
+            this.sanityReverts(i); // Convoluted way to check reverts
+        }
+        i = imax << 1; // Changes sign bit, but should not over/underflow
+        i = imin << 1; // Changes sign bit, but should not over/underflow
+    }
+
+    function testFloat() external pure {
+        console2.log('Float.testFloat()');
+    }
+}